package org.hl7.fhir.r5.fhirpath;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Base64;
import java.util.Calendar;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.fhir.ucum.Decimal;
import org.fhir.ucum.Pair;
import org.fhir.ucum.UcumException;
import org.hl7.fhir.exceptions.DefinitionException;
import org.hl7.fhir.exceptions.FHIRException;
import org.hl7.fhir.exceptions.PathEngineException;
import org.hl7.fhir.instance.model.api.IIdType;
import org.hl7.fhir.r5.conformance.profile.ProfileUtilities;
import org.hl7.fhir.r5.conformance.profile.ProfileUtilities.SourcedChildDefinitions;
import org.hl7.fhir.r5.context.ContextUtilities;
import org.hl7.fhir.r5.context.IWorkerContext;
import org.hl7.fhir.r5.elementmodel.ObjectConverter;
import org.hl7.fhir.r5.fhirpath.ExpressionNode.CollectionStatus;
import org.hl7.fhir.r5.fhirpath.ExpressionNode.Function;
import org.hl7.fhir.r5.fhirpath.ExpressionNode.Kind;
import org.hl7.fhir.r5.fhirpath.ExpressionNode.Operation;
import org.hl7.fhir.r5.fhirpath.FHIRLexer.FHIRLexerException;
import org.hl7.fhir.r5.fhirpath.FHIRPathUtilityClasses.ClassTypeInfo;
import org.hl7.fhir.r5.fhirpath.FHIRPathUtilityClasses.FHIRConstant;
import org.hl7.fhir.r5.fhirpath.FHIRPathUtilityClasses.FunctionDetails;
import org.hl7.fhir.r5.fhirpath.FHIRPathUtilityClasses.TypedElementDefinition;
import org.hl7.fhir.r5.fhirpath.TypeDetails.ProfiledType;
import org.hl7.fhir.r5.model.Base;
import org.hl7.fhir.r5.model.BaseDateTimeType;
import org.hl7.fhir.r5.model.BooleanType;
import org.hl7.fhir.r5.model.CanonicalType;
import org.hl7.fhir.r5.model.CodeType;
import org.hl7.fhir.r5.model.CodeableConcept;
import org.hl7.fhir.r5.model.Constants;
import org.hl7.fhir.r5.model.DateTimeType;
import org.hl7.fhir.r5.model.DateType;
import org.hl7.fhir.r5.model.DecimalType;
import org.hl7.fhir.r5.model.Element;
import org.hl7.fhir.r5.model.ElementDefinition;
import org.hl7.fhir.r5.model.ElementDefinition.TypeRefComponent;
import org.hl7.fhir.r5.model.Identifier;
import org.hl7.fhir.r5.model.IntegerType;
import org.hl7.fhir.r5.model.Property;
import org.hl7.fhir.r5.model.Property.PropertyMatcher;
import org.hl7.fhir.r5.model.Quantity;
import org.hl7.fhir.r5.model.Resource;
import org.hl7.fhir.r5.model.StringType;
import org.hl7.fhir.r5.model.StructureDefinition;
import org.hl7.fhir.r5.model.StructureDefinition.StructureDefinitionKind;
import org.hl7.fhir.r5.model.StructureDefinition.TypeDerivationRule;
import org.hl7.fhir.r5.model.TimeType;
import org.hl7.fhir.r5.model.TypeConvertor;
import org.hl7.fhir.r5.model.ValueSet;
import org.hl7.fhir.r5.terminologies.utilities.ValidationResult;
import org.hl7.fhir.utilities.CommaSeparatedStringBuilder;
import org.hl7.fhir.utilities.DateTimeUtil;
import org.hl7.fhir.utilities.FhirPublication;
import org.hl7.fhir.utilities.MarkDownProcessor;
import org.hl7.fhir.utilities.MergedList;
import org.hl7.fhir.utilities.MergedList.MergeNode;
import org.hl7.fhir.utilities.SourceLocation;
import org.hl7.fhir.utilities.Utilities;
import org.hl7.fhir.utilities.VersionUtilities;
import org.hl7.fhir.utilities.fhirpath.FHIRPathConstantEvaluationMode;
import org.hl7.fhir.utilities.i18n.I18nConstants;
import org.hl7.fhir.utilities.validation.ValidationOptions;
import org.hl7.fhir.utilities.xhtml.NodeType;
import org.hl7.fhir.utilities.xhtml.XhtmlNode;

import ca.uhn.fhir.model.api.TemporalPrecisionEnum;
import ca.uhn.fhir.util.ElementUtil;

/*
  Copyright (c) 2011+, HL7, Inc.
  All rights reserved.

  Redistribution and use in source and binary forms, with or without modification, 
  are permitted provided that the following conditions are met:

 * Redistributions of source code must retain the above copyright notice, this 
     list of conditions and the following disclaimer.
 * Redistributions in binary form must reproduce the above copyright notice, 
     this list of conditions and the following disclaimer in the documentation 
     and/or other materials provided with the distribution.
 * Neither the name of HL7 nor the names of its contributors may be used to 
     endorse or promote products derived from this software without specific 
     prior written permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND 
  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
  INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
  POSSIBILITY OF SUCH DAMAGE.

 */


/**
 * 
 * @author Grahame Grieve
 *
 */
public class FHIRPathEngine {

  public class ExtensionDefinition {

    private boolean root;
    private StructureDefinition sd;
    private ElementDefinition ed;

    public ExtensionDefinition(boolean root, StructureDefinition sd, ElementDefinition ed) {
      super();
      this.root = root;
      this.sd = sd;
      this.ed = ed;
    }

    public boolean isRoot() {
      return root;
    }

    public StructureDefinition getSd() {
      return sd;
    }

    public ElementDefinition getEd() {
      return ed;
    }

  }

  public class IssueMessage {

    private String message;
    private String id;
    
    public IssueMessage(String message, String id) {
      this.message = message;
      this.id = id;
    }

    public String getMessage() {
      return message;
    }

    public String getId() {
      return id;
    }

  }

  private enum Equality { Null, True, False }
  
  private IWorkerContext worker;
  private IHostApplicationServices hostServices;
  private IDebugTracer tracer;
  private StringBuilder log = new StringBuilder();
  private Set<String> primitiveTypes = new HashSet<String>();
  private Map<String, StructureDefinition> allTypes = new HashMap<String, StructureDefinition>();
  private boolean legacyMode; // some R2 and R3 constraints assume that != is valid for empty sets, so when running for R2/R3, this is set ot true  
  private ValidationOptions terminologyServiceOptions = new ValidationOptions(FhirPublication.R5);
  private ProfileUtilities profileUtilities;
  private String location; // for error messages
  private boolean allowPolymorphicNames;
  private boolean doImplicitStringConversion;
  private boolean liquidMode; // in liquid mode, || terminates the expression and hands the parser back to the host
  private boolean doNotEnforceAsSingletonRule;
  private boolean doNotEnforceAsCaseSensitive;

  /*
   * The FHIRPath engine consults with the HostApplicationServices when an element fails to
   * resolve, in case it's an implicit constant being referred to. it can also do that beforehand,
   * in which case the constant will override any element of the given name. But it will only
   * do that if CheckWithHostServicesBeforeHand is true
   */
  private boolean checkWithHostServicesBeforeHand;
  private boolean allowDoubleQuotes;
  private List<IssueMessage> typeWarnings = new ArrayList<>();
  private boolean emitSQLonFHIRWarning;

  public interface IDebugTracer {

    /**
     * When an expression node is evaluated during execution
     * 
     * @param argument
     * @param focus
     * @return
     */
    public void traceExpression(ExecutionContext context, List<Base> focus, List<Base> result, ExpressionNode exp);

    /**
     * When an Operation expression node is evaluated during execution
     * 
     * @param argument
     * @param focus
     * @return
     */
    public void traceOperationExpression(ExecutionContext context, List<Base> focus, List<Base> result, ExpressionNode exp);
  }

  /**
   * @param worker - used when validating paths (@check), and used doing value set membership when executing tests (once that's defined)
   */
  public FHIRPathEngine(IWorkerContext worker) {
    this(worker, new ProfileUtilities(worker, null, null));
  }

  public FHIRPathEngine(IWorkerContext worker, ProfileUtilities utilities) {
    super();
    this.worker = worker;
    profileUtilities = utilities; 
    for (StructureDefinition sd : worker.fetchResourcesByType(StructureDefinition.class)) {
      if (sd.getDerivation() == TypeDerivationRule.SPECIALIZATION && sd.getKind() != StructureDefinitionKind.LOGICAL) {
        allTypes.put(sd.getName(), sd);
      }
      if (sd.getDerivation() == TypeDerivationRule.SPECIALIZATION && sd.getKind() == StructureDefinitionKind.PRIMITIVETYPE) { 
        primitiveTypes.add(sd.getName());
      }
    }
    initFlags();
    cu = new ContextUtilities(worker);
  }

  private void initFlags() {
    if (!VersionUtilities.isR5VerOrLater(worker.getVersion())) {
      doNotEnforceAsCaseSensitive = true;
      doNotEnforceAsSingletonRule = true;
    }
  }

  // --- 3 methods to override in children -------------------------------------------------------
  // if you don't override, it falls through to the using the base reference implementation 
  // HAPI overrides to these to support extending the base model

  public IHostApplicationServices getHostServices() {
    return hostServices;
  }


  public void setHostServices(IHostApplicationServices constantResolver) {
    this.hostServices = constantResolver;
  }

  public IDebugTracer getTracer() {
    return tracer;
  }

  public void setTracer(IDebugTracer tracer) {
    this.tracer = tracer;
  }

  public String getLocation() {
    return location;
  }


  public void setLocation(String location) {
    this.location = location;
  }


  /**
   * Given an item, return all the children that conform to the pattern described in name
   * 
   * Possible patterns:
   *  - a simple name (which may be the base of a name with [] e.g. value[x])
   *  - a name with a type replacement e.g. valueCodeableConcept
   *  - * which means all children
   *  - ** which means all descendants
   *  
   * @param item
   * @param name
   * @param result
   * @throws FHIRException 
   */
  protected void getChildrenByName(Base item, String name, List<Base> result) throws FHIRException {
    String tn = null;
    if (isAllowPolymorphicNames()) {
      // we'll look to see whether we have a polymorphic name 
      for (Property p : item.children()) {
        if (p.getName().endsWith("[x]")) {
          String n = p.getName().substring(0, p.getName().length()-3);
          if (name.startsWith(n)) {
            tn = name.substring(n.length());
            name = n;
            break;            
          }
        }
      }
    }
    Base[] list = item.listChildrenByName(name, false);
    if (list != null) {
      for (Base v : list) {
        if (v != null && (tn == null || v.fhirType().equalsIgnoreCase(tn))) {
          result.add(filterIdType(v));
        }
      }
    }
  }

  private Base filterIdType(Base v) {
    if (v instanceof IIdType) {
      return (Base) ((IIdType) v).toUnqualifiedVersionless().withResourceType(null);
    }
    return v;
  }
  public boolean isLegacyMode() {
    return legacyMode;
  }


  public void setLegacyMode(boolean legacyMode) {
    this.legacyMode = legacyMode;
  }


  public boolean isDoImplicitStringConversion() {
    return doImplicitStringConversion;
  }

  public void setDoImplicitStringConversion(boolean doImplicitStringConversion) {
    this.doImplicitStringConversion = doImplicitStringConversion;
  }

  public boolean isDoNotEnforceAsSingletonRule() {
    return doNotEnforceAsSingletonRule;
  }

  public void setDoNotEnforceAsSingletonRule(boolean doNotEnforceAsSingletonRule) {
    this.doNotEnforceAsSingletonRule = doNotEnforceAsSingletonRule;
  }

  public boolean isDoNotEnforceAsCaseSensitive() {
    return doNotEnforceAsCaseSensitive;
  }

  public void setDoNotEnforceAsCaseSensitive(boolean doNotEnforceAsCaseSensitive) {
    this.doNotEnforceAsCaseSensitive = doNotEnforceAsCaseSensitive;
  }

  /**
   * The FHIRPath engine consults with the HostApplicationServices when an element fails to
   * resolve, in case it's an implicit constant being referred to. it can also do that beforehand,
   * in which case the constant will override any element of the given name. But it will only
   * do that if checkWithHostServicesBeforeHand is true
   */
  public boolean isCheckWithHostServicesBeforeHand() {
    return checkWithHostServicesBeforeHand;
  }

  public void setCheckWithHostServicesBeforeHand(boolean checkWithHostServicesBeforeHand) {
    this.checkWithHostServicesBeforeHand = checkWithHostServicesBeforeHand;
  }
// --- public API -------------------------------------------------------
  /**
   * Parse a path for later use using execute
   * 
   * @param path
   * @return
   * @throws PathEngineException 
   * @throws Exception
   */
  public ExpressionNode parse(String path) throws FHIRLexerException {
    return parse(path, null);
  }

  public ExpressionNode parse(String path, String name) throws FHIRLexerException {
    FHIRLexer lexer = new FHIRLexer(path, name, false, allowDoubleQuotes);
    if (lexer.done()) {
      throw lexer.error("Path cannot be empty");
    }
    ExpressionNode result = parseExpression(lexer, true);
    if (!lexer.done()) {
      throw lexer.error("Premature ExpressionNode termination at unexpected token \""+lexer.getCurrent()+"\"");
    }
    result.check();
    return result;    
  }

  public static class ExpressionNodeWithOffset {
    private int offset;
    private ExpressionNode node;
    public ExpressionNodeWithOffset(int offset, ExpressionNode node) {
      super();
      this.offset = offset;
      this.node = node;
    }
    public int getOffset() {
      return offset;
    }
    public ExpressionNode getNode() {
      return node;
    }

  }
  /**
   * Parse a path for later use using execute
   * 
   * @param path
   * @return
   * @throws PathEngineException 
   * @throws Exception
   */
  public ExpressionNodeWithOffset parsePartial(String path, int i) throws FHIRLexerException {
    FHIRLexer lexer = new FHIRLexer(path, i, allowDoubleQuotes);
    if (lexer.done()) {
      throw lexer.error("Path cannot be empty");
    }
    ExpressionNode result = parseExpression(lexer, true);
    result.check();
    return new ExpressionNodeWithOffset(lexer.getCurrentStart(), result);    
  }

  /**
   * Parse a path that is part of some other syntax
   *  
   * @return
   * @throws PathEngineException 
   * @throws Exception
   */
  public ExpressionNode parse(FHIRLexer lexer) throws FHIRLexerException {
    ExpressionNode result = parseExpression(lexer, true);
    result.check();
    return result;    
  }

  /**
   * check that paths referred to in the ExpressionNode are valid
   * 
   * xPathStartsWithValueRef is a hack work around for the fact that FHIR Path sometimes needs a different starting point than the xpath
   * 
   * returns a list of the possible types that might be returned by executing the ExpressionNode against a particular context
   * 
   * @param context - the logical type against which this path is applied
   * @throws DefinitionException
   * @throws PathEngineException 
   * @if the path is not valid
   */
  public TypeDetails check(Object appContext, String rootResourceType, String resourceType, String context, ExpressionNode expr) throws FHIRLexerException, PathEngineException, DefinitionException {
    return check(appContext, rootResourceType, resourceType, context, expr, null);
  }

  /**
   * check that paths referred to in the ExpressionNode are valid
   * 
   * xPathStartsWithValueRef is a hack work around for the fact that FHIR Path sometimes needs a different starting point than the xpath
   * 
   * returns a list of the possible types that might be returned by executing the ExpressionNode against a particular context
   * 
   * @param context - the logical type against which this path is applied
   * @throws DefinitionException
   * @throws PathEngineException 
   * @if the path is not valid
   */
  public TypeDetails check(Object appContext, String rootResourceType, String resourceType, String context, ExpressionNode expr, Set<ElementDefinition> elementDependencies) throws FHIRLexerException, PathEngineException, DefinitionException {

    // if context is a path that refers to a type, do that conversion now 
    TypeDetails types; 
    if (context == null) {
      types = null; // this is a special case; the first path reference will have to resolve to something in the context
    } else if (!context.contains(".")) {
      StructureDefinition sd = worker.fetchTypeDefinition(context);
      if (sd == null) {
        throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT, context);        
      }
      types = new TypeDetails(CollectionStatus.SINGLETON, sd.getUrl());
    } else {
      String ctxt = context.substring(0, context.indexOf('.'));
      if (Utilities.isAbsoluteUrl(resourceType)) {
        ctxt = resourceType; //.substring(0, resourceType.lastIndexOf("/")+1)+ctxt;
      }
      StructureDefinition sd = cu.findType(ctxt);
      if (sd == null) {
        throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT, context);
      }
      List<ElementDefinitionMatch> edl = getElementDefinition(sd, context, true, expr);
      if (edl.size() == 0) {
        throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT_ELEMENT, context);
      }
      if (edl.size() > 1) {
        throw new Error("Not handled here yet");
      }
      ElementDefinitionMatch ed = edl.get(0);
      if (ed.fixedType != null) { 
        types = new TypeDetails(CollectionStatus.SINGLETON, ed.fixedType);
      } else if (ed.getDefinition().getType().isEmpty() || isAbstractType(ed.getDefinition().getType())) { 
        types = new TypeDetails(CollectionStatus.SINGLETON, ctxt+"#"+context);
      } else {
        types = new TypeDetails(CollectionStatus.SINGLETON);
        for (TypeRefComponent t : ed.getDefinition().getType()) { 
          types.addType(t.getCode());
        }
      }
    }

    return executeType(new ExecutionTypeContext(appContext, rootResourceType, resourceType, types, types), types, expr, elementDependencies, true, false, expr);
  }
  
  /**
   * check that paths referred to in the ExpressionNode are valid
   * 
   * xPathStartsWithValueRef is a hack work around for the fact that FHIR Path sometimes needs a different starting point than the xpath
   * 
   * returns a list of the possible types that might be returned by executing the ExpressionNode against a particular context
   * 
   * @param context - the logical type against which this path is applied
   * @throws DefinitionException
   * @throws PathEngineException 
   * @if the path is not valid
   */
  public TypeDetails checkOnTypes(Object appContext, String rootResourceType, String resourceType, List<String> typeList, ExpressionNode expr, List<IssueMessage> warnings) throws FHIRLexerException, PathEngineException, DefinitionException {
    typeWarnings.clear();

    // if context is a path that refers to a type, do that conversion now 
    TypeDetails types = new TypeDetails(CollectionStatus.SINGLETON);
    for (String t : typeList) {
      if (!t.contains(".")) {
        StructureDefinition sd = worker.fetchTypeDefinition(t);
        if (sd == null) {
          throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT, t);        
        }
        types.addType(sd.getUrl());
      } else {
        boolean checkTypeName = false;
        String ctxt = null;
        if (t.contains("#")) {
          ctxt = t.substring(0, t.indexOf('#'));
          t = t.substring(t.indexOf('#')+1);
        } else if (Utilities.isAbsoluteUrl(t)) {
          ctxt = t;
          t = ctxt.substring(ctxt.lastIndexOf("/")+1);
          checkTypeName = true;
        } else {
          ctxt = t.substring(0, t.indexOf('.'));
        }
        StructureDefinition sd = cu.findType(ctxt);
        if (sd == null) {
          throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT, t);
        }
        String tn = checkTypeName ? sd.getSnapshot().getElementFirstRep().getPath() : t;          

        List<ElementDefinitionMatch> edl = getElementDefinition(sd, tn, true, expr);
        if (edl.size() == 0) {
          throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT_ELEMENT, t);
        }
        if (edl.size() > 1) {
          throw new Error("not handled here either");
        }
        ElementDefinitionMatch ed = edl.get(0);
        if (ed.fixedType != null) { 
          types.addType(ed.fixedType);
        } else if (ed.getDefinition().getType().isEmpty() || isAbstractType(ed.getDefinition().getType())) { 
          types.addType(sd.getType()+"#"+t);
        } else {
          for (TypeRefComponent tt : ed.getDefinition().getType()) { 
            types.addType(tt.getCode());
          }
        }
      }
    }
    TypeDetails res = executeType(new ExecutionTypeContext(appContext, rootResourceType, resourceType, types, types), types, expr, null, true, false, expr);
    warnings.addAll(typeWarnings);
    return res;
  }

  public TypeDetails checkOnTypes(Object appContext, String rootResourceType, String resourceType, TypeDetails types, ExpressionNode expr, List<IssueMessage> warnings) throws FHIRLexerException, PathEngineException, DefinitionException {
    typeWarnings.clear();
    TypeDetails res = executeType(new ExecutionTypeContext(appContext, rootResourceType, resourceType, types, types), types, expr, null, true, false, expr);
    warnings.addAll(typeWarnings);
    return res;
  }
  
  public TypeDetails checkOnTypes(Object appContext, String rootResourceType, String resourceType, TypeDetails types, ExpressionNode expr, List<IssueMessage> warnings, boolean canBeNone) throws FHIRLexerException, PathEngineException, DefinitionException {
    typeWarnings.clear();
    TypeDetails res = executeType(new ExecutionTypeContext(appContext, rootResourceType, resourceType, types, types), types, expr, null, true, canBeNone, expr);
    warnings.addAll(typeWarnings);
    return res;
  }
  
  /**
   * check that paths referred to in the ExpressionNode are valid
   * 
   * xPathStartsWithValueRef is a hack work around for the fact that FHIR Path sometimes needs a different starting point than the xpath
   * 
   * returns a list of the possible types that might be returned by executing the ExpressionNode against a particular context
   * 
   * @throws DefinitionException
   * @throws PathEngineException 
   * @if the path is not valid
   */
  public TypeDetails check(Object appContext, String rootResourceType, String resourceType, List<String> resourceTypes, ExpressionNode expr, Set<ElementDefinition> elementDependencies) throws FHIRLexerException, PathEngineException, DefinitionException {

    // if context is a path that refers to a type, do that conversion now 
    TypeDetails types = null;
    for (String rt : resourceTypes) {
      if (types == null) {
        types = new TypeDetails(CollectionStatus.SINGLETON, rt);
      } else {
        types.addType(rt);
      }
    }

    return executeType(new ExecutionTypeContext(appContext, rootResourceType, resourceType, types, types), types, expr, elementDependencies, true, false, expr);
  }

  private FHIRException makeExceptionPlural(Integer num, ExpressionNode holder, String constName, Object... args) {
    String fmt = worker.formatMessagePlural(num, constName, args);
    if (location != null) {
      fmt = fmt + " "+worker.formatMessagePlural(num, I18nConstants.FHIRPATH_LOCATION, location);
    }
    if (holder != null) {      
       return new PathEngineException(fmt, constName, holder.getStart(), holder.toString());
    } else {
      return new PathEngineException(fmt, constName);
    }
  }
  
  private FHIRException makeException(ExpressionNode holder, String constName, Object... args) {
    String fmt = worker.formatMessage(constName, args);
    if (location != null) {
      fmt = fmt + " "+worker.formatMessage(I18nConstants.FHIRPATH_LOCATION, location);
    }
    if (holder != null) {      
       return new PathEngineException(fmt, constName, holder.getStart(), holder.toString());
    } else {
      return new PathEngineException(fmt, constName);
    }
  }

  public TypeDetails check(Object appContext, String rootResourceType, StructureDefinition sd, String context, ExpressionNode expr) throws FHIRLexerException, PathEngineException, DefinitionException {
    // if context is a path that refers to a type, do that conversion now 
    TypeDetails types; 
    if (!context.contains(".")) {
      types = new TypeDetails(CollectionStatus.SINGLETON, sd.getUrl());
    } else {
      List<ElementDefinitionMatch> edl = getElementDefinition(sd, context, true, expr);
      if (edl.size() == 0) {
        throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT_ELEMENT, context);
      }
      if (edl.size() > 1) {
        throw new Error("Unhandled case?");
      }
      ElementDefinitionMatch ed = edl.get(0);
      if (ed.fixedType != null) { 
        types = new TypeDetails(CollectionStatus.SINGLETON, ed.fixedType);
      } else if (ed.getDefinition().getType().isEmpty() || isAbstractType(ed.getDefinition().getType())) { 
        types = new TypeDetails(CollectionStatus.SINGLETON, sd.getUrl()+"#"+context);
      } else {
        types = new TypeDetails(CollectionStatus.SINGLETON);
        for (TypeRefComponent t : ed.getDefinition().getType()) { 
          types.addType(t.getCode());
        }
      }
    }

    return executeType(new ExecutionTypeContext(appContext, rootResourceType, sd.getUrl(), types, types), types, expr, null, true, false, expr);
  }

  public TypeDetails check(Object appContext, String rootResourceType, StructureDefinition sd, ExpressionNode expr) throws FHIRLexerException, PathEngineException, DefinitionException {
    // if context is a path that refers to a type, do that conversion now 
    TypeDetails types = null; // this is a special case; the first path reference will have to resolve to something in the context
    return executeType(new ExecutionTypeContext(appContext, rootResourceType, sd == null ? null : sd.getUrl(), null, types), types, expr, null, true, false, expr);
  }

  public TypeDetails check(Object appContext, String rootResourceType, String resourceType, String context, String expr) throws FHIRLexerException, PathEngineException, DefinitionException {
    return check(appContext, rootResourceType, resourceType, context, parse(expr));
  }

  private Integer compareDateTimeElements(Base theL, Base theR, boolean theEquivalenceTest) {
    DateTimeType left = theL instanceof DateTimeType ? (DateTimeType) theL : new DateTimeType(theL.primitiveValue()); 
    DateTimeType right = theR instanceof DateTimeType ? (DateTimeType) theR : new DateTimeType(theR.primitiveValue()); 

    if (theEquivalenceTest) {
      return left.equalsUsingFhirPathRules(right) == Boolean.TRUE ? 0 : 1;
    }

    if (left.getPrecision().ordinal() > TemporalPrecisionEnum.DAY.ordinal()) {
      left.setTimeZoneZulu(true);
    }
    if (right.getPrecision().ordinal() > TemporalPrecisionEnum.DAY.ordinal()) {
      right.setTimeZoneZulu(true);
    }
    return BaseDateTimeType.compareTimes(left, right, null);
  }

  private Integer compareTimeElements(Base theL, Base theR, boolean theEquivalenceTest) {
    TimeType left = theL instanceof TimeType ? (TimeType) theL : new TimeType(theL.primitiveValue()); 
    TimeType right = theR instanceof TimeType ? (TimeType) theR : new TimeType(theR.primitiveValue()); 

    if (left.getHour() < right.getHour()) {
      return -1;
    } else if (left.getHour() > right.getHour()) {
      return 1;
      // hour is not a valid precision 
      //    } else if (dateLeft.getPrecision() == TemporalPrecisionEnum.YEAR && dateRight.getPrecision() == TemporalPrecisionEnum.YEAR) {
      //      return 0;
      //    } else if (dateLeft.getPrecision() == TemporalPrecisionEnum.HOUR || dateRight.getPrecision() == TemporalPrecisionEnum.HOUR) {
      //      return null;
    }

    if (left.getMinute() < right.getMinute()) {
      return -1;
    } else if (left.getMinute() > right.getMinute()) {
      return 1;
    } else if (left.getPrecision() == TemporalPrecisionEnum.MINUTE && right.getPrecision() == TemporalPrecisionEnum.MINUTE) {
      return 0;
    } else if (left.getPrecision() == TemporalPrecisionEnum.MINUTE || right.getPrecision() == TemporalPrecisionEnum.MINUTE) {
      return null;
    }

    if (left.getSecond() < right.getSecond()) {
      return -1;
    } else if (left.getSecond() > right.getSecond()) {
      return 1;
    } else {
      return 0;
    }

  }


  /**
   * evaluate a path and return the matching elements
   * 
   * @param base - the object against which the path is being evaluated
   * @param ExpressionNode - the parsed ExpressionNode statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public List<Base> evaluate(Base base, ExpressionNode ExpressionNode) throws FHIRException {
    List<Base> list = new ArrayList<Base>();
    if (base != null) {
      list.add(base);
    }
    log = new StringBuilder();
    return execute(new ExecutionContext(null, base != null && base.isResource() ? base : null, base != null && base.isResource() ? base : null, base, base), list, ExpressionNode, true);
  }


  /**
   * evaluate a path and return the matching elements
   * 
   * @param base - the object against which the path is being evaluated
   * @param ExpressionNode - the parsed ExpressionNode statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public List<Base> evaluate(Object appContext, Base base, ExpressionNode ExpressionNode) throws FHIRException {
    List<Base> list = new ArrayList<Base>();
    if (base != null) {
      list.add(base);
    }
    log = new StringBuilder();
    return execute(new ExecutionContext(appContext, base != null && base.isResource() ? base : null, base != null && base.isResource() ? base : null, base, base), list, ExpressionNode, true);
  }
  
  /**
   * evaluate a path and return the matching elements
   * 
   * @param base - the object against which the path is being evaluated
   * @param path - the FHIR Path statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public List<Base> evaluate(Base base, String path) throws FHIRException {
    ExpressionNode exp = parse(path);
    List<Base> list = new ArrayList<Base>();
    if (base != null) {
      list.add(base);
    }
    log = new StringBuilder();
    return execute(new ExecutionContext(null, base.isResource() ? base : null, base.isResource() ? base : null, base, base), list, exp, true);
  }

  /**
   * evaluate a path and return the matching elements
   * 
   * @param base - the object against which the path is being evaluated
   * @param ExpressionNode - the parsed ExpressionNode statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public List<Base> evaluate(Object appContext, Resource focusResource, Resource rootResource, Base base, ExpressionNode ExpressionNode) throws FHIRException {
    List<Base> list = new ArrayList<Base>();
    if (base != null) {
      list.add(base);
    }
    log = new StringBuilder();
    return execute(new ExecutionContext(appContext, focusResource, rootResource, base, base), list, ExpressionNode, true);
  }

  /**
   * evaluate a path and return the matching elements
   * 
   * @param base - the object against which the path is being evaluated
   * @param expressionNode - the parsed ExpressionNode statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public List<Base> evaluate(Object appContext, Base focusResource, Base rootResource, Base base, ExpressionNode expressionNode) throws FHIRException {
    List<Base> list = new ArrayList<Base>();
    if (base != null) {
      list.add(base);
    }
    log = new StringBuilder();
    return execute(new ExecutionContext(appContext, focusResource, rootResource, base, base), list, expressionNode, true);
  }

  /**
   * evaluate a path and return the matching elements
   * 
   * @param base - the object against which the path is being evaluated
   * @param path - the FHIR Path statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public List<Base> evaluate(Object appContext, Resource focusResource, Resource rootResource, Base base, String path) throws FHIRException {
    ExpressionNode exp = parse(path);
    List<Base> list = new ArrayList<Base>();
    if (base != null) {
      list.add(base);
    }
    log = new StringBuilder();
    return execute(new ExecutionContext(appContext, focusResource, rootResource, base, base), list, exp, true);
  }

  /**
   * evaluate a path and return true or false (e.g. for an invariant)
   * 
   * @param base - the object against which the path is being evaluated
   * @param path - the FHIR Path statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public boolean evaluateToBoolean(Resource focusResource, Resource rootResource, Base base, String path) throws FHIRException {
    return convertToBoolean(evaluate(null, focusResource, rootResource, base, path));
  }

  /**
   * evaluate a path and return true or false (e.g. for an invariant)
   * 
   * @param base - the object against which the path is being evaluated
   * @return
   * @throws FHIRException 
   * @
   */
  public boolean evaluateToBoolean(Resource focusResource, Resource rootResource, Base base, ExpressionNode node) throws FHIRException {
    return convertToBoolean(evaluate(null, focusResource, rootResource, base, node));
  }

  /**
   * evaluate a path and return true or false (e.g. for an invariant)
   * 
   * @param appInfo - application context
   * @param base - the object against which the path is being evaluated
   * @return
   * @throws FHIRException 
   * @
   */
  public boolean evaluateToBoolean(Object appInfo, Resource focusResource, Resource rootResource, Base base, ExpressionNode node) throws FHIRException {
    return convertToBoolean(evaluate(appInfo, focusResource, rootResource, base, node));
  }

  /**
   * evaluate a path and return true or false (e.g. for an invariant)
   * 
   * @param base - the object against which the path is being evaluated
   * @return
   * @throws FHIRException 
   * @
   */
  public boolean evaluateToBoolean(Object appInfo, Base focusResource, Base rootResource, Base base, ExpressionNode node) throws FHIRException {
    return convertToBoolean(evaluate(appInfo, focusResource, rootResource, base, node));
  }

  /**
   * evaluate a path and a string containing the outcome (for display)
   * 
   * @param base - the object against which the path is being evaluated
   * @param path - the FHIR Path statement to use
   * @return
   * @throws FHIRException 
   * @
   */
  public String evaluateToString(Base base, String path) throws FHIRException {
    return convertToString(evaluate(base, path));
  }

  public String evaluateToString(Object appInfo, Base focusResource, Base rootResource, Base base, ExpressionNode node) throws FHIRException {
    return convertToString(evaluate(appInfo, focusResource, rootResource, base, node));
  }

  /**
   * worker routine for converting a set of objects to a string representation
   * 
   * @param items - result from @evaluate
   * @return
   */
  public String convertToString(List<Base> items) {
    StringBuilder b = new StringBuilder();
    boolean first = true;
    for (Base item : items) {
      if (first)  {
        first = false;
      } else {
        b.append(',');
      }

      b.append(convertToString(item));
    }
    return b.toString();
  }

  public String convertToString(Base item) {
    if (item instanceof IIdType) {
      return ((IIdType)item).getIdPart();
    } else if (item.isPrimitive()) {
      return item.primitiveValue();
    } else if (item.fhirType().equals("Quantity")) {
      Quantity q = makeQuantity(item);
      if (q.hasUnit() && Utilities.existsInList(q.getUnit(), "year", "years", "month", "months", "week", "weeks", "day", "days", "hour", "hours", "minute", "minutes", "second", "seconds", "millisecond", "milliseconds")
          && (!q.hasSystem() || q.getSystem().equals("http://unitsofmeasure.org"))) {
        return (q.hasValue() ? q.getValue().toPlainString() : "")+" "+q.getUnit();
      }
      if ("http://unitsofmeasure.org".equals(q.getSystem())) {
        String u = "'"+q.getCode()+"'";
        return (q.hasValue() ? q.getValue().toPlainString() : "")+" "+u;
      } else {
        return item.toString();
      }
    } else
      return item.toString();
  }

  /**
   * worker routine for converting a set of objects to a boolean representation (for invariants)
   * 
   * @param items - result from @evaluate
   * @return
   */
  public boolean convertToBoolean(List<Base> items) {
    if (items == null) {
      return false;
    } else if (items.size() == 1 && items.get(0) instanceof BooleanType) {
      return ((BooleanType) items.get(0)).getValue();
    } else if (items.size() == 1 && items.get(0).isBooleanPrimitive()) { // element model
      return Boolean.valueOf(items.get(0).primitiveValue());
    } else { 
      return items.size() > 0;
    }
  }


  private void log(String name, List<Base> contents) {
    if (hostServices == null || !hostServices.log(name, contents)) {
      if (log.length() > 0) {
        log.append("; ");
      }
      log.append(name);
      log.append(": ");
      boolean first = true;
      for (Base b : contents) {
        if (first) {
          first = false;
        } else {
          log.append(",");
        }
        log.append(convertToString(b));
      }
    }
  }

  public String forLog() {
    if (log.length() > 0) {
      return " ("+log.toString()+")";
    } else {
      return "";
    }
  }

  public class ExecutionContext {
    private Object appInfo;
    private Base focusResource;
    private Base rootResource;
    private Base context;
    private Base thisItem;
    private List<Base> total;
    private int index;
    private Map<String, List<Base>> definedVariables;

    public ExecutionContext(Object appInfo, Base resource, Base rootResource, Base context, Base thisItem) {
      this.appInfo = appInfo;
      this.context = context;
      this.focusResource = resource; 
      this.rootResource = rootResource; 
      this.thisItem = thisItem;
      this.index = 0;
    }
    public Base getFocusResource() {
      return focusResource;
    }
    public Base getRootResource() {
      return rootResource;
    }
    public Base getThisItem() {
      return thisItem;
    }
    public List<Base> getTotal() {
      return total;
    }

    public void next() {
      index++;
    }
    public Base getIndex() {
      return new IntegerType(index);
    }

    public ExecutionContext setIndex(int i) {
      index = i;
      return this;
    }

    public boolean hasDefinedVariable(String name) {
      return definedVariables != null && definedVariables.containsKey(name);
    }

    public List<Base> getDefinedVariable(String name) {
      return definedVariables == null ? makeNull() : definedVariables.get(name);
    }

    public void setDefinedVariable(String name, List<Base> value) {
      if (isSystemVariable(name))
        throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_REDEFINE_VARIABLE, name), I18nConstants.FHIRPATH_REDEFINE_VARIABLE);

      if (definedVariables == null) {
        definedVariables = new HashMap<String, List<Base>>();
      } else {
        if (definedVariables.containsKey(name)) {
          // Can't do this, so throw an error
          throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_REDEFINE_VARIABLE, name), I18nConstants.FHIRPATH_REDEFINE_VARIABLE);
        }
      }

      definedVariables.put(name, value);
    }
  }

  private static class ExecutionTypeContext {
    private Object appInfo; 
    private String resource;
    private TypeDetails context;
    private TypeDetails thisItem;
    private TypeDetails total;
    private Map<String, TypeDetails> definedVariables;
    private String rootResource;

    public ExecutionTypeContext(Object appInfo, String rootResource, String resource, TypeDetails context, TypeDetails thisItem) {
      super();
      this.appInfo = appInfo;
      this.rootResource = rootResource;
      this.resource = resource;
      this.context = context;
      this.thisItem = thisItem;

    }
    public String getResource() {
      return resource;
    }
    public TypeDetails getThisItem() {
      return thisItem;
    }

    public boolean hasDefinedVariable(String name) {
      return definedVariables != null && definedVariables.containsKey(name);
    }

    public TypeDetails getDefinedVariable(String name) {
      return definedVariables == null ? null : definedVariables.get(name);
    }

    public void setDefinedVariable(String name, TypeDetails value) {
      if (isSystemVariable(name))
        throw new PathEngineException("Redefine of variable "+name, I18nConstants.FHIRPATH_REDEFINE_VARIABLE);

      if (definedVariables == null) {
        definedVariables = new HashMap<String, TypeDetails>();
      } else {
        if (definedVariables.containsKey(name)) {
          // Can't do this, so throw an error
          throw new PathEngineException("Redefine of variable "+name, I18nConstants.FHIRPATH_REDEFINE_VARIABLE);
        }
      }

      definedVariables.put(name, value);
    }
  }

  private ExpressionNode parseExpression(FHIRLexer lexer, boolean proximal) throws FHIRLexerException {
    ExpressionNode result = new ExpressionNode(lexer.nextId());
    ExpressionNode wrapper = null;
    SourceLocation c = lexer.getCurrentStartLocation().copy();
    result.setStart(lexer.getCurrentStartLocation().copy());
    // special: +/- represents a unary operation at this point, but cannot be a feature of the lexer, since that's not always true.
    // so we back correct for both +/- and as part of a numeric constant below.

    // special: +/- represents a unary operation at this point, but cannot be a feature of the lexer, since that's not always true.
    // so we back correct for both +/- and as part of a numeric constant below.
    if (Utilities.existsInList(lexer.getCurrent(), "-", "+")) {
      wrapper = new ExpressionNode(lexer.nextId());
      wrapper.setKind(Kind.Unary);
      wrapper.setOperation(ExpressionNode.Operation.fromCode(lexer.take()));
      wrapper.setStart(lexer.getCurrentLocation().copy());
      wrapper.setProximal(proximal);
    }

    if (lexer.getCurrent() == null) {
      throw lexer.error("Expression terminated unexpectedly");
    } else if (lexer.isConstant()) {
      boolean isString = lexer.isStringConstant();
      if (!isString && (lexer.getCurrent().startsWith("-") || lexer.getCurrent().startsWith("+"))) {
        // the grammar says that this is a unary operation; it affects the correct processing order of the inner operations
        wrapper = new ExpressionNode(lexer.nextId());
        wrapper.setKind(Kind.Unary);
        wrapper.setOperation(ExpressionNode.Operation.fromCode(lexer.getCurrent().substring(0, 1)));
        wrapper.setProximal(proximal);
        wrapper.setStart(lexer.getCurrentLocation().copy());
        lexer.setCurrent(lexer.getCurrent().substring(1));
      }
      result.setEnd(lexer.getCurrentLocation().copy());
      result.setConstant(processConstant(lexer));
      result.setKind(Kind.Constant);
      if (!isString && !lexer.done() && (result.getConstant() instanceof IntegerType || result.getConstant() instanceof DecimalType) && (lexer.isStringConstant() || lexer.hasToken("year", "years", "month", "months", "week", "weeks", "day", "days", "hour", "hours", "minute", "minutes", "second", "seconds", "millisecond", "milliseconds"))) {
        // it's a quantity
        String ucum = null;
        String unit = null;
        if (lexer.hasToken("year", "years", "month", "months", "week", "weeks", "day", "days", "hour", "hours", "minute", "minutes", "second", "seconds", "millisecond", "milliseconds")) {
          String s = lexer.take();
          unit = s;
          if (s.equals("year") || s.equals("years")) {
            // this is not the UCUM year
          } else if (s.equals("month") || s.equals("months")) {
            // this is not the UCUM month
          } else if (s.equals("week") || s.equals("weeks")) {
            ucum = "wk";
          } else if (s.equals("day") || s.equals("days")) {
            ucum = "d";
          } else if (s.equals("hour") || s.equals("hours")) {
            ucum = "h";
          } else if (s.equals("minute") || s.equals("minutes")) {
            ucum = "min";
          } else if (s.equals("second") || s.equals("seconds")) {
            ucum = "s";
          } else { // (s.equals("millisecond") || s.equals("milliseconds"))
            ucum = "ms";
          } 
        } else {
          result.setEnd(lexer.getCurrentLocation().copy());
          ucum = lexer.readConstant("units");
        }
        result.setConstant(new Quantity().setValue(new BigDecimal(result.getConstant().primitiveValue())).setUnit(unit).setSystem(ucum == null ? null : "http://unitsofmeasure.org").setCode(ucum));
      }
    } else if ("(".equals(lexer.getCurrent())) {
      lexer.next();
      result.setKind(Kind.Group);
      result.setGroup(parseExpression(lexer, true));
      if (!")".equals(lexer.getCurrent())) {
        throw lexer.error("Found "+lexer.getCurrent()+" expecting a \")\"");
      }
      result.setEnd(lexer.getCurrentLocation().copy());
      lexer.next();
    } else {
      if (!lexer.isToken() && !lexer.getCurrent().startsWith("`")) {
        throw lexer.error("Found "+lexer.getCurrent()+" expecting a token name");
      }
      if (lexer.isFixedName()) {
        result.setEnd(lexer.getCurrentLocation().copy());
        result.setName(lexer.readFixedName("Path Name"));
      } else {
        result.setEnd(lexer.getCurrentLocation().copy());
        result.setName(lexer.take());
      }
      if (!result.checkName()) {
        throw lexer.error("Found "+result.getName()+" expecting a valid token name");
      }
      if ("(".equals(lexer.getCurrent())) {
        Function f = Function.fromCode(result.getName());
        FunctionDetails details = null;
        if (f == null) {
          if (hostServices != null) {
            details = hostServices.resolveFunction(this, result.getName());
          }
          if (details == null) {
            throw lexer.error("The name "+result.getName()+" is not a valid function name");
          }
          f = Function.Custom;
        }
        result.setKind(Kind.Function);
        result.setFunction(f);
        lexer.next();
        while (!")".equals(lexer.getCurrent())) { 
          result.getParameters().add(parseExpression(lexer, true));
          if (",".equals(lexer.getCurrent())) {
            lexer.next();
          } else if (!")".equals(lexer.getCurrent())) {
            throw lexer.error("The token "+lexer.getCurrent()+" is not expected here - either a \",\" or a \")\" expected");
          }
        }
        lexer.next();
        checkParameters(lexer, c, result, details);
      } else {
        result.setKind(Kind.Name);
      }
    }
    ExpressionNode focus = result;
    if ("[".equals(lexer.getCurrent())) {
      ExpressionNode item = new ExpressionNode(lexer.nextId());
      item.setKind(Kind.Function);
      item.setFunction(ExpressionNode.Function.Item);
      item.setStart(lexer.getCurrentStartLocation().copy());
      lexer.next();
      item.getParameters().add(parseExpression(lexer, true));
      if (!lexer.getCurrent().equals("]")) {
        throw lexer.error("The token "+lexer.getCurrent()+" is not expected here - a \"]\" expected");
      }
      item.setEnd(lexer.getCurrentLocation().copy());
      lexer.next();
      result.setInner(item);
      focus = item;
    }
    if (".".equals(lexer.getCurrent())) {
      lexer.next();
      focus.setInner(parseExpression(lexer, false));
    }
    result.setProximal(proximal);
    if (proximal) {
      while (lexer.isOp()) {
        focus.setOperation(ExpressionNode.Operation.fromCode(lexer.getCurrent()));
        focus.setOpStart(lexer.getCurrentStartLocation().copy());
        focus.setOpEnd(lexer.getCurrentLocation().copy());
        lexer.next();
        focus.setOpNext(parseExpression(lexer, false));
        focus = focus.getOpNext();
      }
      result = organisePrecedence(lexer, result);
    }
    if (wrapper != null) {
      wrapper.setOpNext(result);
      result.setProximal(false);
      result = wrapper;
    }
    return result;
  }

  private ExpressionNode organisePrecedence(FHIRLexer lexer, ExpressionNode node) {
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Times, Operation.DivideBy, Operation.Div, Operation.Mod)); 
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Plus, Operation.Minus, Operation.Concatenate)); 
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Union)); 
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.LessThan, Operation.Greater, Operation.LessOrEqual, Operation.GreaterOrEqual));
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Is, Operation.As));
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Equals, Operation.Equivalent, Operation.NotEquals, Operation.NotEquivalent));
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.In, Operation.Contains, Operation.MemberOf));
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.And));
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Xor, Operation.Or));
    // last: implies
    return node;
  }
   

  private ExpressionNode gatherPrecedence(FHIRLexer lexer, ExpressionNode start, EnumSet<Operation> ops) {
    //    work : boolean;
    //    focus, node, group : ExpressionNode;

    assert(start.isProximal());

    // is there anything to do?
    boolean work = false;
    ExpressionNode focus = start.getOpNext();
    if (ops.contains(start.getOperation())) {
      while (focus != null && focus.getOperation() != null) {
        work = work || !ops.contains(focus.getOperation());
        focus = focus.getOpNext();
      }
    } else {
      while (focus != null && focus.getOperation() != null) {
        work = work || ops.contains(focus.getOperation());
        focus = focus.getOpNext();
      }
    }  
    if (!work) {
      return start;
    }

    // entry point: tricky
    ExpressionNode group;
    if (ops.contains(start.getOperation())) {
      group = newGroup(lexer, start);
      group.setProximal(true);
      focus = start;
      start = group;
    } else {
      ExpressionNode node = start;

      focus = node.getOpNext();
      while (!ops.contains(focus.getOperation())) {
        node = focus;
        focus = focus.getOpNext();
      }
      group = newGroup(lexer, focus);
      node.setOpNext(group);
    }

    // now, at this point:
    //   group is the group we are adding to, it already has a .group property filled out.
    //   focus points at the group.group
    do {
      // run until we find the end of the sequence
      while (ops.contains(focus.getOperation())) {
        focus = focus.getOpNext();
      }
      if (focus.getOperation() != null) {
        group.setOperation(focus.getOperation());
        group.setOpNext(focus.getOpNext());
        group.setOpStart(focus.getOpStart());
        group.setOpEnd(focus.getOpEnd());
        focus.setOperation(null);
        focus.setOpNext(null);
        // now look for another sequence, and start it
        ExpressionNode node = group;
        focus = group.getOpNext();
        if (focus != null) { 
          while (focus != null && !ops.contains(focus.getOperation())) {
            node = focus;
            focus = focus.getOpNext();
          }
          if (focus != null) { // && (focus.Operation in Ops) - must be true 
            group = newGroup(lexer, focus);
            node.setOpNext(group);
          }
        }
      }
    }
    while (focus != null && focus.getOperation() != null);
    return start;
  }


  private ExpressionNode newGroup(FHIRLexer lexer, ExpressionNode next) {
    ExpressionNode result = new ExpressionNode(lexer.nextId());
    result.setKind(Kind.Group);
    result.setGroup(next);
    result.getGroup().setProximal(true);
    return result;
  }

  private Base processConstant(FHIRLexer lexer) throws FHIRLexerException {
    if (lexer.isStringConstant()) {
      return new StringType(processConstantString(lexer.take(), lexer)).noExtensions();
    } else if (Utilities.isInteger(lexer.getCurrent())) {
      return new IntegerType(lexer.take()).noExtensions();
    } else if (Utilities.isDecimal(lexer.getCurrent(), false)) {
      return new DecimalType(lexer.take()).noExtensions();
    } else if (Utilities.existsInList(lexer.getCurrent(), "true", "false")) {
      return new BooleanType(lexer.take()).noExtensions();
    } else if (lexer.getCurrent().equals("{}")) {
      lexer.take();
      return null;
    } else if (lexer.getCurrent().startsWith("%") || lexer.getCurrent().startsWith("@")) {
      return new FHIRConstant(lexer.take());
    } else {
      throw lexer.error("Invalid Constant "+lexer.getCurrent());
    }
  }

  //  procedure CheckParamCount(c : integer);
  //  begin
  //    if exp.Parameters.Count <> c then
  //      raise lexer.error('The function "'+exp.name+'" requires '+inttostr(c)+' parameters', offset);
  //  end;

  private boolean checkParamCount(FHIRLexer lexer, SourceLocation location, ExpressionNode exp, int count) throws FHIRLexerException {
    if (exp.getParameters().size() != count) {
      throw lexer.error("The function \""+exp.getName()+"\" requires "+Integer.toString(count)+" parameters", location.toString(), location);
    }
    return true;
  }

  private boolean checkParamCount(FHIRLexer lexer, SourceLocation location, ExpressionNode exp, int countMin, int countMax) throws FHIRLexerException {
    if (exp.getParameters().size() < countMin || exp.getParameters().size() > countMax) {
      throw lexer.error("The function \""+exp.getName()+"\" requires between "+Integer.toString(countMin)+" and "+Integer.toString(countMax)+" parameters", location.toString(), location);
    }
    return true;
  }

  private boolean checkParameters(FHIRLexer lexer, SourceLocation location, ExpressionNode exp, FunctionDetails details) throws FHIRLexerException {
    switch (exp.getFunction()) {
    case Empty: return checkParamCount(lexer, location, exp, 0);
    case Not: return checkParamCount(lexer, location, exp, 0);
    case Exists: return checkParamCount(lexer, location, exp, 0, 1);
    case SubsetOf: return checkParamCount(lexer, location, exp, 1);
    case SupersetOf: return checkParamCount(lexer, location, exp, 1);
    case IsDistinct: return checkParamCount(lexer, location, exp, 0);
    case Distinct: return checkParamCount(lexer, location, exp, 0);
    case Count: return checkParamCount(lexer, location, exp, 0);
    case Where: return checkParamCount(lexer, location, exp, 1);
    case Select: return checkParamCount(lexer, location, exp, 1);
    case All: return checkParamCount(lexer, location, exp, 0, 1);
    case Repeat: return checkParamCount(lexer, location, exp, 1);
    case Aggregate: return checkParamCount(lexer, location, exp, 1, 2);
    case Item: return checkParamCount(lexer, location, exp, 1);
    case As: return checkParamCount(lexer, location, exp, 1);
    case OfType: return checkParamCount(lexer, location, exp, 1);
    case Type: return checkParamCount(lexer, location, exp, 0);
    case Is: return checkParamCount(lexer, location, exp, 1);
    case Single: return checkParamCount(lexer, location, exp, 0);
    case First: return checkParamCount(lexer, location, exp, 0);
    case Last: return checkParamCount(lexer, location, exp, 0);
    case Tail: return checkParamCount(lexer, location, exp, 0);
    case Skip: return checkParamCount(lexer, location, exp, 1);
    case Take: return checkParamCount(lexer, location, exp, 1);
    case Union: return checkParamCount(lexer, location, exp, 1);
    case Combine: return checkParamCount(lexer, location, exp, 1);
    case Intersect: return checkParamCount(lexer, location, exp, 1);
    case Exclude: return checkParamCount(lexer, location, exp, 1);
    case Iif: return checkParamCount(lexer, location, exp, 2,3);
    case Lower: return checkParamCount(lexer, location, exp, 0);
    case Upper: return checkParamCount(lexer, location, exp, 0);
    case ToChars: return checkParamCount(lexer, location, exp, 0);
    case IndexOf : return checkParamCount(lexer, location, exp, 1);
    case Substring: return checkParamCount(lexer, location, exp, 1, 2);
    case StartsWith: return checkParamCount(lexer, location, exp, 1);
    case EndsWith: return checkParamCount(lexer, location, exp, 1);
    case Matches: return checkParamCount(lexer, location, exp, 1);
    case MatchesFull: return checkParamCount(lexer, location, exp, 1);
    case ReplaceMatches: return checkParamCount(lexer, location, exp, 2);
    case Contains: return checkParamCount(lexer, location, exp, 1);
    case Replace: return checkParamCount(lexer, location, exp, 2);
    case Length: return checkParamCount(lexer, location, exp, 0);
    case Children: return checkParamCount(lexer, location, exp, 0);
    case Descendants: return checkParamCount(lexer, location, exp, 0);
    case MemberOf: return checkParamCount(lexer, location, exp, 1);
    case Trace: return checkParamCount(lexer, location, exp, 1, 2);
    case DefineVariable: return checkParamCount(lexer, location, exp, 1, 2);
    case Check: return checkParamCount(lexer, location, exp, 2);
    case Today: return checkParamCount(lexer, location, exp, 0);
    case Now: return checkParamCount(lexer, location, exp, 0);
    case Resolve: return checkParamCount(lexer, location, exp, 0);
    case Extension: return checkParamCount(lexer, location, exp, 1);
    case AllFalse: return checkParamCount(lexer, location, exp, 0);
    case AnyFalse: return checkParamCount(lexer, location, exp, 0);
    case AllTrue: return checkParamCount(lexer, location, exp, 0);
    case AnyTrue: return checkParamCount(lexer, location, exp, 0);
    case HasValue: return checkParamCount(lexer, location, exp, 0);
    case Encode: return checkParamCount(lexer, location, exp, 1);
    case Decode: return checkParamCount(lexer, location, exp, 1);
    case Escape: return checkParamCount(lexer, location, exp, 1);
    case Unescape: return checkParamCount(lexer, location, exp, 1);
    case Trim: return checkParamCount(lexer, location, exp, 0);
    case Split: return checkParamCount(lexer, location, exp, 1);
    case Join: return checkParamCount(lexer, location, exp, 0, 1);    
    case HtmlChecks1: return checkParamCount(lexer, location, exp, 0);
    case HtmlChecks2: return checkParamCount(lexer, location, exp, 0);
    case Comparable: return checkParamCount(lexer, location, exp, 1);
    case ToInteger: return checkParamCount(lexer, location, exp, 0);
    case ToDecimal: return checkParamCount(lexer, location, exp, 0);
    case ToString: return checkParamCount(lexer, location, exp, 0);
    case ToQuantity: return checkParamCount(lexer, location, exp, 0);
    case ToBoolean: return checkParamCount(lexer, location, exp, 0);
    case ToDateTime: return checkParamCount(lexer, location, exp, 0);
    case ToTime: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToInteger: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToDecimal: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToString: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToQuantity: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToBoolean: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToDateTime: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToDate: return checkParamCount(lexer, location, exp, 0);
    case ConvertsToTime: return checkParamCount(lexer, location, exp, 0);
    case ConformsTo: return checkParamCount(lexer, location, exp, 1);
    case Round: return checkParamCount(lexer, location, exp, 0, 1); 
    case Sqrt: return checkParamCount(lexer, location, exp, 0); 
    case Abs: return checkParamCount(lexer, location, exp, 0);
    case Ceiling:  return checkParamCount(lexer, location, exp, 0);
    case Exp:  return checkParamCount(lexer, location, exp, 0);
    case Floor:  return checkParamCount(lexer, location, exp, 0);
    case Ln:  return checkParamCount(lexer, location, exp, 0);
    case Log:  return checkParamCount(lexer, location, exp, 1);
    case Power:  return checkParamCount(lexer, location, exp, 1);
    case Truncate: return checkParamCount(lexer, location, exp, 0);
    case Sort: return checkParamCount(lexer, location, exp, 0, 10);
    case Coalesce: return checkParamCount(lexer, location, exp, 1, Integer.MAX_VALUE); // un-bounded number of parameters
    case LowBoundary: return checkParamCount(lexer, location, exp, 0, 1);
    case HighBoundary: return checkParamCount(lexer, location, exp, 0, 1);
    case Precision: return checkParamCount(lexer, location, exp, 0);
    case hasTemplateIdOf: return checkParamCount(lexer, location, exp, 1);
    case Custom: return checkParamCount(lexer, location, exp, details.getMinParameters(), details.getMaxParameters());
    }
    return false;
  }

  private List<Base> execute(ExecutionContext inContext, List<Base> focus, ExpressionNode exp, boolean atEntry) throws FHIRException {
    ExecutionContext context = contextForParameter(inContext);
    List<Base> work = new ArrayList<Base>();
    switch (exp.getKind()) {
    case Unary:
      work.add(new IntegerType(0));
      break;
    case Name:
      if (atEntry && exp.getName().equals("$this")) {
        work.add(context.getThisItem());
      } else if (atEntry && exp.getName().equals("$total")) {
        work.addAll(context.getTotal());
      } else if (atEntry && exp.getName().equals("$index")) {
        work.add(context.getIndex());
      } else {
        for (Base item : focus) {
          List<Base> outcome = execute(context, item, exp, atEntry);
          for (Base base : outcome) {
            if (base != null) {
              work.add(base);
            }
          }
        }     
      }
      traceExpression(focus, exp, context, work);
      break;
    case Function:
      List<Base> work2 = evaluateFunction(context, focus, exp);
      work.addAll(work2);
      traceExpression(focus, exp, context, work);
      break;
    case Constant:
      work.addAll(resolveConstant(context, exp.getConstant(), FHIRPathConstantEvaluationMode.EXPLICIT, exp));
      traceExpression(focus, exp, context, work);
      break;
    case Group:
      work2 = execute(context, focus, exp.getGroup(), atEntry);
      work.addAll(work2);
      break;
    }

    if (exp.getInner() != null) {
      work = execute(context, work, exp.getInner(), false);
    }

    if (exp.isProximal() && exp.getOperation() != null) {
      ExpressionNode next = exp.getOpNext();
      ExpressionNode last = exp;
      while (next != null) {
        context = contextForParameter(inContext);
        List<Base> work2 = preOperate(work, last.getOperation(), exp);
        if (work2 != null) {
          work = work2;
        }
        else if (last.getOperation() == Operation.Is || last.getOperation() == Operation.As) {
          work2 = executeTypeName(context, focus, next, false);
          work = operate(context, work, last.getOperation(), work2, last);
          if (tracer != null) { tracer.traceOperationExpression(context, focus, work, last); }
        } else {
          work2 = execute(context, focus, next, true);
          work = operate(context, work, last.getOperation(), work2, last);
          if (tracer != null) { tracer.traceOperationExpression(context, focus, work, last); }
        }
        last = next;
        next = next.getOpNext();
      }
    }
    return work;
  }

  private void traceExpression(List<Base> focus, ExpressionNode exp, ExecutionContext context, List<Base> work) {
    if (tracer == null) { return; }
    tracer.traceExpression(context, focus, work, exp);
  }

  private List<Base> executeTypeName(ExecutionContext context, List<Base> focus, ExpressionNode next, boolean atEntry) {
    List<Base> result = new ArrayList<Base>();
    if (next.getInner() != null) {
      result.add(new StringType(next.getName()+"."+next.getInner().getName()));
    } else { 
      result.add(new StringType(next.getName()));
    }
    return result;
  }


  private List<Base> preOperate(List<Base> left, Operation operation, ExpressionNode expr) throws PathEngineException {
    if (left.size() == 0) {
      return null;
    }
    switch (operation) {
    case And:
      return isBoolean(left, false) ? makeBoolean(false) : null;
    case Or:
      return isBoolean(left, true) ? makeBoolean(true) : null;
    case Implies:
      Equality v = asBool(left, expr); 
      return v == Equality.False ? makeBoolean(true) : null;
    default: 
      return null;
    }
  }

  private List<Base> makeBoolean(boolean b) {
    List<Base> res = new ArrayList<Base>();
    res.add(new BooleanType(b).noExtensions());
    return res;
  }

  public static Quantity makeQuantity(Base base) {
    if (base == null) {
      return null;
    }
    if (base instanceof Quantity) {
      return (Quantity) base;
    }
    if (base instanceof org.hl7.fhir.r5.elementmodel.Element) {
      return ObjectConverter.readAsQuantity((org.hl7.fhir.r5.elementmodel.Element) base);
    }
    return null;
  }

  private List<Base> makeNull() {
    List<Base> res = new ArrayList<Base>();
    return res;
  }

  private TypeDetails executeTypeName(ExecutionTypeContext context, TypeDetails focus, ExpressionNode exp, boolean atEntry) throws PathEngineException, DefinitionException {
    return new TypeDetails(CollectionStatus.SINGLETON, exp.getName());
  }

  private TypeDetails executeType(ExecutionTypeContext inContext, TypeDetails focus, ExpressionNode exp, Set<ElementDefinition> elementDependencies, boolean atEntry, boolean canBeNone, ExpressionNode container) throws PathEngineException, DefinitionException {
    ExecutionTypeContext context = contextForParameter(inContext);
    TypeDetails result = new TypeDetails(null);
    switch (exp.getKind()) {
    case Name:
      if (atEntry && exp.getName().equals("$this")) {
        result.update(context.getThisItem());
      } else if (atEntry && exp.getName().equals("$total")) {
        result.update(anything(CollectionStatus.UNORDERED));
      } else if (atEntry && exp.getName().equals("$index")) {
        result.addType(TypeDetails.FP_Integer);
      } else if (atEntry && focus == null) {
        result.update(executeContextType(context, exp.getName(), exp, FHIRPathConstantEvaluationMode.NOVALUE));
      } else {
        for (String s : focus.getTypes()) {
          result.update(executeType(s, exp, atEntry, focus, elementDependencies));
        }
        if (result.hasNoTypes()) {
          if (!canBeNone) { 
            throw makeException(exp, I18nConstants.FHIRPATH_UNKNOWN_NAME, exp.getName(), focus.describe());
          } else {
            // return result;
          }
        }
      }
      doSQLOnFHIRCheck(result, exp);
      break;
    case Function:
      result.update(evaluateFunctionType(context, focus, exp, elementDependencies, container));
      break;
    case Unary:
      result.addType(TypeDetails.FP_Integer);
      result.addType(TypeDetails.FP_Decimal);
      result.addType(TypeDetails.FP_Quantity);
      break;
    case Constant:
      result.update(resolveConstantType(context, exp.getConstant(), exp, FHIRPathConstantEvaluationMode.EXPLICIT));
      break;
    case Group:
      result.update(executeType(context, focus, exp.getGroup(), elementDependencies, atEntry, canBeNone, exp));
    }
    exp.setTypes(result);

    if (exp.getInner() != null) {
      result = executeType(context, result, exp.getInner(), elementDependencies, false, false, exp);
    }

    if (exp.isProximal() && exp.getOperation() != null) {
      ExpressionNode next = exp.getOpNext();
      ExpressionNode last = exp;
      while (next != null) {
        context = contextForParameter(inContext);
        TypeDetails work;
        if (last.getOperation() == Operation.Is || last.getOperation() == Operation.As) {
          work = executeTypeName(context, focus, next, atEntry);
        } else {
          work = executeType(context, focus, next, elementDependencies, atEntry, canBeNone, exp);
        }
        result = operateTypes(result, last.getOperation(), work, last);
        last = next;
        next = next.getOpNext();
      }
      exp.setOpTypes(result);
    }
    return result;
  }

  private void doSQLOnFHIRCheck(TypeDetails focus, ExpressionNode expr) {
    if (emitSQLonFHIRWarning) {
      // special Logic for SQL-on-FHIR:
      if (focus.isChoice()) {
        if (expr.getInner() == null || expr.getInner().getFunction() != Function.OfType) {
          typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_CHOICE_NO_TYPE_SPECIFIER, expr.toString()), I18nConstants.FHIRPATH_CHOICE_NO_TYPE_SPECIFIER));
        }
      } else if (expr.getInner() != null && expr.getInner().getFunction() == Function.OfType) {
        typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_CHOICE_SPURIOUS_TYPE_SPECIFIER, expr.toString()), I18nConstants.FHIRPATH_CHOICE_SPURIOUS_TYPE_SPECIFIER));
      }
    }
  }
  private List<Base> resolveConstant(ExecutionContext context, Base constant, FHIRPathConstantEvaluationMode mode, ExpressionNode expr) throws PathEngineException {
    if (constant == null) {
      return new ArrayList<Base>();
    }
    if (!(constant instanceof FHIRConstant)) {
      return new ArrayList<Base>(Arrays.asList(constant));
    }
    FHIRConstant c = (FHIRConstant) constant;
    if (c.getValue().startsWith("%")) {
      String varName = c.getValue().substring(1);
      if (context.hasDefinedVariable(varName)) {
        return context.getDefinedVariable(varName);
      }
      return resolveConstant(context, c.getValue(), mode, expr);
    } else if (c.getValue().startsWith("@")) {
      return new ArrayList<Base>(Arrays.asList(processDateConstant(context.appInfo, c.getValue().substring(1), expr)));
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONSTANT, c.getValue());
    }
  }

  private Base processDateConstant(Object appInfo, String value, ExpressionNode expr) throws PathEngineException {
    String date = null;
    String time = null;
    String tz = null;

    TemporalPrecisionEnum temp = null;

    if (value.startsWith("T")) {
      time = value.substring(1);
    } else if (!value.contains("T")) {
      date = value;
    } else {
      String[] p = value.split("T");
      date = p[0];
      if (p.length > 1) {
        time = p[1];
      }
    }

    if (time != null) {
      int i = time.indexOf("-");
      if (i == -1) {
        i = time.indexOf("+");
      }
      if (i == -1) {
        i = time.indexOf("Z");
      }
      if (i > -1) {
        tz = time.substring(i);
        time = time.substring(0, i);
      }

      if (time.length() == 2) {
        time = time+":00:00";
        temp = TemporalPrecisionEnum.MINUTE;
      } else if (time.length() == 5) {
        temp = TemporalPrecisionEnum.MINUTE;
        time = time+":00";
      } else if (time.contains(".")) {
        temp = TemporalPrecisionEnum.MILLI;
      } else {
        temp = TemporalPrecisionEnum.SECOND;
      }
    }

    if (date == null) {
      if (tz != null) {
        throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONTEXT, value);
      } else {
        TimeType tt = new TimeType(time);
        tt.setPrecision(temp);
        return tt.noExtensions();
      }
    } else if (time != null) {
      DateTimeType dt = new DateTimeType(date+"T"+time+(tz == null ? "" : tz));
      dt.setPrecision(temp);
      return dt.noExtensions();
    } else { 
      return new DateType(date).noExtensions();
    }
  }

  static boolean isSystemVariable(String name){
    if (name.equals("sct"))
      return true;
    if (name.equals("loinc"))
      return true;
    if (name.equals("ucum"))
      return true;
    if (name.equals("resource"))
      return true;
    if (name.equals("rootResource"))
      return true;
    if (name.equals("context"))
      return true;
    return false;
  }

  private List<Base> resolveConstant(ExecutionContext context, String s, FHIRPathConstantEvaluationMode mode, ExpressionNode expr) throws PathEngineException {
    if (s.equals("%sct")) {
      return new ArrayList<Base>(Arrays.asList(new StringType("http://snomed.info/sct").noExtensions()));
    } else if (s.equals("%loinc")) {
      return new ArrayList<Base>(Arrays.asList(new StringType("http://loinc.org").noExtensions()));
    } else if (s.equals("%ucum")) {
      return new ArrayList<Base>(Arrays.asList(new StringType("http://unitsofmeasure.org").noExtensions()));
    } else if (s.equals("%resource")) {
      if (context.focusResource == null) {
        throw makeException(expr, I18nConstants.FHIRPATH_CANNOT_USE, "%resource", "no focus resource");
      }
      return new ArrayList<Base>(Arrays.asList(context.focusResource));
    } else if (s.equals("%rootResource")) {
      if (context.rootResource == null) {
        throw makeException(expr, I18nConstants.FHIRPATH_CANNOT_USE, "%rootResource", "no focus rootResource");
      }
      return new ArrayList<Base>(Arrays.asList(context.rootResource));
    } else if (s.equals("%context")) {
      return new ArrayList<Base>(Arrays.asList(context.context));
    } else if (s.equals("%us-zip")) {
      return new ArrayList<Base>(Arrays.asList(new StringType("[0-9]{5}(-[0-9]{4}){0,1}").noExtensions()));
    } else if (s.startsWith("%`vs-")) {
      return new ArrayList<Base>(Arrays.asList(new StringType("http://hl7.org/fhir/ValueSet/"+s.substring(5, s.length()-1)+"").noExtensions()));
    } else if (s.startsWith("%`cs-")) {
      return new ArrayList<Base>(Arrays.asList(new StringType("http://hl7.org/fhir/"+s.substring(5, s.length()-1)+"").noExtensions()));
    } else if (s.startsWith("%`ext-")) {
      return new ArrayList<Base>(Arrays.asList(new StringType("http://hl7.org/fhir/StructureDefinition/"+s.substring(6, s.length()-1)).noExtensions()));
    } else if (hostServices == null) {
      throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONSTANT, s);
    } else {
      return hostServices.resolveConstant(this, context.appInfo, mode == FHIRPathConstantEvaluationMode.EXPLICIT ? s.substring(1) : s, mode);
    }
  }


  private String processConstantString(String s, FHIRLexer lexer) throws FHIRLexerException {
    StringBuilder b = new StringBuilder();
    int i = 1;
    while (i < s.length()-1) {
      char ch = s.charAt(i);
      if (ch == '\\') {
        i++;
        switch (s.charAt(i)) {
        case 't': 
          b.append('\t');
          break;
        case 'r':
          b.append('\r');
          break;
        case 'n': 
          b.append('\n');
          break;
        case 'f': 
          b.append('\f');
          break;
        case '\'':
          b.append('\'');
          break;
        case '"':
          b.append('"');
          break;
        case '`':
          b.append('`');
          break;
        case '\\': 
          b.append('\\');
          break;
        case '/': 
          b.append('/');
          break;
        case 'u':
          i++;
          int uc = Integer.parseInt(s.substring(i, i+4), 16);
          b.append(Character.toString(uc));
          i = i + 3;
          break;
        default:
          throw lexer.error("Unknown FHIRPath character escape \\"+s.charAt(i));
        }
        i++;
      } else {
        b.append(ch);
        i++;
      }
    }
    return b.toString();
  }


  private List<Base> operate(ExecutionContext context, List<Base> left, Operation operation, List<Base> right, ExpressionNode holder) throws FHIRException {
    switch (operation) {
    case Equals: return opEquals(left, right, holder);
    case Equivalent: return opEquivalent(left, right, holder);
    case NotEquals: return opNotEquals(left, right, holder);
    case NotEquivalent: return opNotEquivalent(left, right, holder);
    case LessThan: return opLessThan(left, right, holder);
    case Greater: return opGreater(left, right, holder);
    case LessOrEqual: return opLessOrEqual(left, right, holder);
    case GreaterOrEqual: return opGreaterOrEqual(left, right, holder);
    case Union: return opUnion(left, right, holder);
    case In: return opIn(left, right, holder);
    case MemberOf: return opMemberOf(context, left, right, holder);
    case Contains: return opContains(left, right, holder);
    case Or:  return opOr(left, right, holder);
    case And:  return opAnd(left, right, holder);
    case Xor: return opXor(left, right, holder);
    case Implies: return opImplies(left, right, holder);
    case Plus: return opPlus(left, right, holder);
    case Times: return opTimes(left, right, holder);
    case Minus: return opMinus(left, right, holder);
    case Concatenate: return opConcatenate(left, right, holder);
    case DivideBy: return opDivideBy(left, right, holder);
    case Div: return opDiv(left, right, holder);
    case Mod: return opMod(left, right, holder);
    case Is: return opIs(left, right, holder);
    case As: return opAs(left, right, holder);
    default: 
      throw new Error("Not Done Yet: "+operation.toCode());
    }
  }

  private List<Base> opAs(List<Base> left, List<Base> right, ExpressionNode expr) {
    List<Base> result = new ArrayList<>();
    if (right.size() != 1) {
      return result;
    } else {
      String tn = convertToString(right);
      if (!isKnownType(tn)) {
        throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_INVALID_TYPE, tn), I18nConstants.FHIRPATH_INVALID_TYPE);
      }
      if (!doNotEnforceAsSingletonRule && left.size() > 1) {
        throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_AS_COLLECTION, left.size(), expr.toString()), I18nConstants.FHIRPATH_AS_COLLECTION); 
      }
      for (Base nextLeft : left) {
        if (compareTypeNames(tn, nextLeft.fhirType())) {
          result.add(nextLeft);
        }
      }
    }
    return result;
  }

  private boolean compareTypeNames(String left, String right) {
    if (doNotEnforceAsCaseSensitive) {
      return left.equalsIgnoreCase(right);            
    } else {
      return left.equals(right);      
    }
  }

  private boolean isKnownType(String tn) {
    if (!tn.contains(".")) {
      if (Utilities.existsInList(tn, "String", "Boolean", "Integer", "Decimal", "Quantity", "DateTime", "Time", "SimpleTypeInfo", "ClassInfo")) {
        return true;
      }
      try {
        return worker.fetchTypeDefinition(tn) != null;
      } catch (Exception e) {
        return false;
      }
    }
    String[] t = tn.split("\\.");
    if (t.length != 2) {
      return false;
    }
    if ("System".equals(t[0])) {
      return Utilities.existsInList(t[1], "String", "Boolean", "Integer", "Decimal", "Quantity", "DateTime", "Time", "SimpleTypeInfo", "ClassInfo");
    } else if ("FHIR".equals(t[0])) {      
      try {
        return worker.fetchTypeDefinition(t[1]) != null;
      } catch (Exception e) {
        return false;
      }
    } else if ("CDA".equals(t[0])) {      
      try {
        return worker.fetchTypeDefinition(Utilities.pathURL(Constants.NS_CDA_ROOT, "StructureDefinition", t[1])) != null;
      } catch (Exception e) {
        return false;
      }
    } else {
      return false;
    }
  }

  private List<Base> opIs(List<Base> left, List<Base> right, ExpressionNode expr) {
    List<Base> result = new ArrayList<Base>();
    if (left.size() == 0 || right.size() == 0) {
    } else if (left.size() != 1 || right.size() != 1) 
      result.add(new BooleanType(false).noExtensions());
    else {
      String tn = convertToString(right);
      if (left.get(0) instanceof org.hl7.fhir.r5.elementmodel.Element) {
        result.add(new BooleanType(left.get(0).hasType(tn)).noExtensions());
      } else if ((left.get(0) instanceof Element) && ((Element) left.get(0)).isDisallowExtensions()) {
        result.add(new BooleanType(Utilities.capitalize(left.get(0).fhirType()).equals(tn) || ("System."+Utilities.capitalize(left.get(0).fhirType())).equals(tn)).noExtensions());
      } else {
        if (left.get(0).fhirType().equals(tn)) {
          result.add(new BooleanType(true).noExtensions());
        } else {
          StructureDefinition sd = worker.fetchTypeDefinition(left.get(0).fhirType());
          while (sd != null) {
            if (tn.equals(sd.getType())) {
              return makeBoolean(true);
            }
            sd = worker.fetchResource(StructureDefinition.class, sd.getBaseDefinition(), sd);
          }
          return makeBoolean(false);
        }      
      }
    }
    return result;
  }


  private void checkCardinalityForComparabilitySame(TypeDetails left, Operation operation, TypeDetails right, ExpressionNode expr) {
    if (left.isList() && !right.isList()) {
      typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_LEFT, expr.toString()), I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_LEFT));
    } else if (!left.isList() && right.isList()) {
      typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_RIGHT, expr.toString()), I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_RIGHT));
    }
  }

  private void checkCardinalityForSingle(TypeDetails left, Operation operation, TypeDetails right, ExpressionNode expr) {
    if (left.isList()) {
      typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_LEFT, expr.toString()), I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_LEFT));
    } 
    if (right.isList()) {
      typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_RIGHT, expr.toString()), I18nConstants.FHIRPATH_COLLECTION_STATUS_OPERATION_RIGHT));
    }
  }
  
  private TypeDetails operateTypes(TypeDetails left, Operation operation, TypeDetails right, ExpressionNode expr) {
    switch (operation) {
    case Equals: 
      checkCardinalityForComparabilitySame(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Equivalent: 
      checkCardinalityForComparabilitySame(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case NotEquals: 
      checkCardinalityForComparabilitySame(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case NotEquivalent: 
      checkCardinalityForComparabilitySame(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case LessThan: 
      checkCardinalityForSingle(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Greater: 
      checkCardinalityForSingle(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case LessOrEqual: 
      checkCardinalityForSingle(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case GreaterOrEqual: 
      checkCardinalityForSingle(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Is: 
      checkCardinalityForSingle(left, operation, right, expr);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case As: 
      checkCardinalityForSingle(left, operation, right, expr);
      TypeDetails td = new TypeDetails(CollectionStatus.SINGLETON, right.getTypes());
      if (td.typesHaveTargets()) {
        td.addTargets(left.getTargets());
      }
      return td;
    case Union: return left.union(right);
    case Or: return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case And: return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Xor: return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Implies : return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Times: 
      checkCardinalityForSingle(left, operation, right, expr);
      TypeDetails result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer")) {
        result.addType(TypeDetails.FP_Integer);
      } else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal")) {
        result.addType(TypeDetails.FP_Decimal);
      }
      return result;
    case DivideBy: 
      checkCardinalityForSingle(left, operation, right, expr);
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer")) {
        result.addType(TypeDetails.FP_Decimal);
      } else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal")) {
        result.addType(TypeDetails.FP_Decimal);
      }
      return result;
    case Concatenate:
      checkCardinalityForSingle(left, operation, right, expr);
      result = new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
      return result;
    case Plus:
      checkCardinalityForSingle(left, operation, right, expr);
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer")) {
        result.addType(TypeDetails.FP_Integer);
      } else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal")) {
        result.addType(TypeDetails.FP_Decimal);
      } else if (left.hasType(worker, "string", "id", "code", "uri") && right.hasType(worker, "string", "id", "code", "uri")) {
        result.addType(TypeDetails.FP_String);
      } else if (left.hasType(worker, "date", "dateTime", "instant")) {
        if (right.hasType(worker, "Quantity")) {
          result.addType(left.getType());
        } else {
          throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_ARITHMETIC_PLUS, right.getType(), left.getType()), I18nConstants.FHIRPATH_ARITHMETIC_PLUS, expr.getOpStart(), expr.toString()); 
        }
      }
      return result;
    case Minus:
      checkCardinalityForSingle(left, operation, right, expr);
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer")) {
        result.addType(TypeDetails.FP_Integer);
      } else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal")) {
        result.addType(TypeDetails.FP_Decimal);
      } else if (left.hasType(worker, "Quantity") && right.hasType(worker, "Quantity")) {
        result.addType(TypeDetails.FP_Quantity);
      } else if (left.hasType(worker, "date", "dateTime", "instant")) {
        if (right.hasType(worker, "Quantity")) {
          result.addType(left.getType());
        } else {
          throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_ARITHMETIC_MINUS, right.getType(), left.getType()), I18nConstants.FHIRPATH_ARITHMETIC_MINUS, expr.getOpStart(), expr.toString());
        }
      }
      return result;
    case Div: 
    case Mod: 
      checkCardinalityForSingle(left, operation, right, expr);
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer")) {
        result.addType(TypeDetails.FP_Integer);
      } else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal")) {
        result.addType(TypeDetails.FP_Decimal);
      }
      return result;
    case In: return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case MemberOf: return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Contains: return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    default: 
      return null;
    }
  }


  private List<Base> opEquals(List<Base> left, List<Base> right, ExpressionNode expr) {
    if (left.size() == 0 || right.size() == 0) { 
      return new ArrayList<Base>();
    }

    if (left.size() != right.size()) {
      return makeBoolean(false);
    }

    boolean res = true;
    boolean nil = false;
    for (int i = 0; i < left.size(); i++) {
      Boolean eq = doEquals(left.get(i), right.get(i));
      if (eq == null) {
        nil = true;
      } else if (eq == false) { 
        res = false;
        break;
      }
    }
    if (!res) {
      return makeBoolean(res);
    } else if (nil) {
      return new ArrayList<Base>();
    } else {
      return makeBoolean(res);
    }
  }

  private List<Base> opNotEquals(List<Base> left, List<Base> right, ExpressionNode expr) {
    if (!legacyMode && (left.size() == 0 || right.size() == 0)) {
      return new ArrayList<Base>();
    }

    if (left.size() != right.size()) {
      return makeBoolean(true);
    }

    boolean res = true;
    boolean nil = false;
    for (int i = 0; i < left.size(); i++) {
      Boolean eq = doEquals(left.get(i), right.get(i));
      if (eq == null) {
        nil = true;
      } else if (eq == true) { 
        res = false;
        break;
      }
    }
    if (!res) {
      return makeBoolean(res);
    } else if (nil) {
      return new ArrayList<Base>();
    } else {
      return makeBoolean(res);
    }
  }

  private String removeTrailingZeros(String s) {
    if (Utilities.noString(s))
      return "";
    int i = s.length()-1;
    boolean done = false;
    boolean dot = false;
    while (i > 0 && !done) {
      if (s.charAt(i) == '.') {
        i--;
        dot = true;
      } else if (!dot && s.charAt(i) == '0') {
        i--;
      } else {
        done = true;
      }
    }
    return s.substring(0, i+1);
  }

  private boolean decEqual(String left, String right) {
    left = removeTrailingZeros(left);
    right = removeTrailingZeros(right);
    return left.equals(right);
  }

  private Boolean datesEqual(BaseDateTimeType left, BaseDateTimeType right) {
    return left.equalsUsingFhirPathRules(right);
  }

  private Boolean doEquals(Base left, Base right) {
    var lq = makeQuantity(left);
    var rq = makeQuantity(right);
    if (lq instanceof Quantity && rq instanceof Quantity) {
      return qtyEqual(lq, rq);
    } else if (left.hasType("date", "dateTime", "instant") && right.hasType("date", "dateTime", "instant")) { 
      var leftDate = new DateTimeType(left.primitiveValue());
      var rightDate = new DateTimeType(right.primitiveValue());
      return datesEqual(leftDate, rightDate);
    } else if (left instanceof DecimalType || right instanceof DecimalType) { 
      return decEqual(left.primitiveValue(), right.primitiveValue());
    } else if (left.isPrimitive() && right.isPrimitive()) {
      return Base.equals(left.primitiveValue(), right.primitiveValue());
    } else {
      return Base.compareDeep(left, right, false);
    }
  }

  private boolean doEquivalent(Base left, Base right) throws PathEngineException {
    var lq = makeQuantity(left);
    var rq = makeQuantity(right);
    if (lq instanceof Quantity && rq instanceof Quantity) {
      return qtyEquivalent(lq, rq);
    }
    if (left.hasType("integer") && right.hasType("integer")) {
      return doEquals(left, right);
    }
    if (left.hasType("boolean") && right.hasType("boolean")) {
      return doEquals(left, right);
    }
    if (left.hasType("integer", "decimal", "unsignedInt", "positiveInt") && right.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      return Utilities.equivalentNumber(left.primitiveValue(), right.primitiveValue());
    }
    if (left.hasType("date", "dateTime", "time", "instant") && right.hasType("date", "dateTime", "time", "instant")) {
      Integer i = compareDateTimeElements(left, right, true);
      if (i == null) {
        i = 0;
      }
      return i == 0;
    }
    if (left.hasType(FHIR_TYPES_STRING) && right.hasType(FHIR_TYPES_STRING)) {
      return Utilities.equivalent(convertToString(left), convertToString(right));
    }
    if (left.isPrimitive() && right.isPrimitive()) {
      return Utilities.equivalent(left.primitiveValue(), right.primitiveValue());
    }
    if (!left.isPrimitive() && !right.isPrimitive()) {
      MergedList<Property> props = new MergedList<Property>(left.children(), right.children(), new PropertyMatcher());
      for (MergeNode<Property> t : props) {
        if (t.hasLeft() && t.hasRight()) {
          if (t.getLeft().hasValues() && t.getRight().hasValues()) {
            MergedList<Base> values = new MergedList<Base>(t.getLeft().getValues(), t.getRight().getValues());
            for (MergeNode<Base> v : values) {
              if (v.hasLeft() && v.hasRight()) {
                if (!doEquivalent(v.getLeft(), v.getRight())) {
                  return false;
                }
              } else if (v.hasLeft() || v.hasRight()) {
                return false;
              }            
            }
          } else if (t.getLeft().hasValues() || t.getRight().hasValues()) {
            return false;
          }
        } else {
          return false;
        }
      }
      return true;
    } else {
      return false;
    }      
  }

  private Boolean qtyEqual(Quantity left, Quantity right) {
    if (!left.hasValue() && !right.hasValue()) {
      return true;
    }
    if (!left.hasValue() || !right.hasValue()) {
      return null;
    }
    if (worker.getUcumService() != null) {
      Pair dl = qtyToCanonicalPair(left);
      Pair dr = qtyToCanonicalPair(right);
      if (dl != null && dr != null) {
        if (dl.getCode().equals(dr.getCode())) {
          return doEquals(new DecimalType(dl.getValue().asDecimal()), new DecimalType(dr.getValue().asDecimal()));          
        } else {
          return false;
        }
      }
    }
    if (left.hasCode() || right.hasCode()) {
      if (!(left.hasCode() && right.hasCode()) || !left.getCode().equals(right.getCode())) {
        return null;
      }
    } else if (!left.hasUnit() || right.hasUnit()) {
      if (!(left.hasUnit() && right.hasUnit()) || !left.getUnit().equals(right.getUnit())) {
        return null;
      }
    }
    return doEquals(new DecimalType(left.getValue()), new DecimalType(right.getValue()));
  }

  private Pair qtyToCanonicalPair(Quantity q) {
    if (!"http://unitsofmeasure.org".equals(q.getSystem())) {
      return null;
    }
    try {
      Pair p = new Pair(new Decimal(q.getValue().toPlainString()), q.getCode() == null ? "1" : q.getCode());
      Pair c = worker.getUcumService().getCanonicalForm(p);
      return c;
    } catch (UcumException e) {
      return null;
    }
  }

  private DecimalType qtyToCanonicalDecimal(Quantity q) {
    if (!"http://unitsofmeasure.org".equals(q.getSystem())) {
      return null;
    }
    try {
      Pair p = new Pair(new Decimal(q.getValue().toPlainString()), q.getCode() == null ? "1" : q.getCode());
      Pair c = worker.getUcumService().getCanonicalForm(p);
      return new DecimalType(c.getValue().asDecimal());
    } catch (UcumException e) {
      return null;
    }
  }

  private Base pairToQty(Pair p) {
    return new Quantity().setValue(new BigDecimal(p.getValue().toString())).setSystem("http://unitsofmeasure.org").setCode(p.getCode()).noExtensions();
  }


  private Pair qtyToPair(Quantity q) {
    if (!"http://unitsofmeasure.org".equals(q.getSystem())) {
      return null;
    }
    try {
      return new Pair(new Decimal(q.getValue().toPlainString()), q.getCode());
    } catch (UcumException e) {
      return null;
    }
  }


  private Boolean qtyEquivalent(Quantity left, Quantity right) throws PathEngineException {
    if (!left.hasValue() && !right.hasValue()) {
      return true;
    }
    if (!left.hasValue() || !right.hasValue()) {
      return null;
    }
    if (worker.getUcumService() != null) {
      Pair dl = qtyToCanonicalPair(left);
      Pair dr = qtyToCanonicalPair(right);
      if (dl != null && dr != null) {
        if (dl.getCode().equals(dr.getCode())) {
          return doEquivalent(new DecimalType(dl.getValue().asDecimal()), new DecimalType(dr.getValue().asDecimal()));          
        } else {
          return false;
        }
      }
    }
    if (left.hasCode() || right.hasCode()) {
      if (!(left.hasCode() && right.hasCode()) || !left.getCode().equals(right.getCode())) {
        return null;
      }
    } else if (!left.hasUnit() || right.hasUnit()) {
      if (!(left.hasUnit() && right.hasUnit()) || !left.getUnit().equals(right.getUnit())) {
        return null;
      }
    }
    return doEquivalent(new DecimalType(left.getValue()), new DecimalType(right.getValue()));
  }



  private List<Base> opEquivalent(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() != right.size()) {
      return makeBoolean(false);
    }

    boolean res = true;
    for (int i = 0; i < left.size(); i++) {
      boolean found = false;
      for (int j = 0; j < right.size(); j++) {
        if (doEquivalent(left.get(i), right.get(j))) {
          found = true;
          break;
        }
      }
      if (!found) {
        res = false;
        break;
      }
    }
    return makeBoolean(res);
  }

  private List<Base> opNotEquivalent(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() != right.size()) {
      return makeBoolean(true);
    }

    boolean res = true;
    for (int i = 0; i < left.size(); i++) {
      boolean found = false;
      for (int j = 0; j < right.size(); j++) {
        if (doEquivalent(left.get(i), right.get(j))) {
          found = true;
          break;
        }
      }
      if (!found) {
        res = false;
        break;
      }
    }
    return makeBoolean(!res);
  }

  private final static String[] FHIR_TYPES_STRING = new String[] {"string", "uri", "code", "oid", "id", "uuid", "sid", "markdown", "base64Binary", "canonical", "url", "xhtml"};

  private List<Base> opLessThan(List<Base> left, List<Base> right, ExpressionNode expr) throws FHIRException {
    if (left.size() == 0 || right.size() == 0) 
      return new ArrayList<Base>();

    if (left.size() == 1 && right.size() == 1 && left.get(0).isPrimitive() && right.get(0).isPrimitive()) {
      Base l = left.get(0);
      Base r = right.get(0);
      if (l.hasType(FHIR_TYPES_STRING) && r.hasType(FHIR_TYPES_STRING)) { 
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) < 0);
      } else if ((l.hasType("integer") || l.hasType("decimal")) && (r.hasType("integer") || r.hasType("decimal"))) { 
        return makeBoolean(new Double(l.primitiveValue()) < new Double(r.primitiveValue()));
      } else if ((l.hasType("date", "dateTime", "instant")) && (r.hasType("date", "dateTime", "instant"))) {
        Integer i = compareDateTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i < 0);
        }
      } else if ((l.hasType("time")) && (r.hasType("time"))) { 
        Integer i = compareTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i < 0);
        }
      } else {
        throw makeException(expr, I18nConstants.FHIRPATH_CANT_COMPARE, l.fhirType(), r.fhirType());
      }
    } else if (left.size() == 1 && right.size() == 1 && left.get(0).fhirType().equals("Quantity") && right.get(0).fhirType().equals("Quantity") ) {
      List<Base> lUnit = left.get(0).listChildrenByName("code");
      List<Base> rUnit = right.get(0).listChildrenByName("code");
      if (Base.compareDeep(lUnit, rUnit, true)) {
        return opLessThan(left.get(0).listChildrenByName("value"), right.get(0).listChildrenByName("value"), expr);
      } else {
        if (worker.getUcumService() == null) {
          return makeBoolean(false);
        } else {
          var lq = makeQuantity(left.get(0));
          var rq = makeQuantity(right.get(0));
          List<Base> dl = new ArrayList<Base>();
          dl.add(qtyToCanonicalDecimal(lq));
          List<Base> dr = new ArrayList<Base>();
          dr.add(qtyToCanonicalDecimal(rq));
          return opLessThan(dl, dr, expr);
        }
      }
    }
    return new ArrayList<Base>();
  }

  private List<Base> opGreater(List<Base> left, List<Base> right, ExpressionNode expr) throws FHIRException {
    if (left.size() == 0 || right.size() == 0) 
      return new ArrayList<Base>();
    if (left.size() == 1 && right.size() == 1 && left.get(0).isPrimitive() && right.get(0).isPrimitive()) {
      Base l = left.get(0);
      Base r = right.get(0);
      if (l.hasType(FHIR_TYPES_STRING) && r.hasType(FHIR_TYPES_STRING)) {
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) > 0);
      } else if ((l.hasType("integer", "decimal", "unsignedInt", "positiveInt")) && (r.hasType("integer", "decimal", "unsignedInt", "positiveInt"))) { 
        return makeBoolean(new Double(l.primitiveValue()) > new Double(r.primitiveValue()));
      } else if ((l.hasType("date", "dateTime", "instant")) && (r.hasType("date", "dateTime", "instant"))) {
        Integer i = compareDateTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i > 0); 
        }
      } else if ((l.hasType("time")) && (r.hasType("time"))) { 
        Integer i = compareTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i > 0);
        }
      } else {
        throw makeException(expr, I18nConstants.FHIRPATH_CANT_COMPARE, l.fhirType(), r.fhirType());
      }
    } else if (left.size() == 1 && right.size() == 1 && left.get(0).fhirType().equals("Quantity") && right.get(0).fhirType().equals("Quantity") ) {
      List<Base> lUnit = left.get(0).listChildrenByName("unit");
      List<Base> rUnit = right.get(0).listChildrenByName("unit");
      if (Base.compareDeep(lUnit, rUnit, true)) {
        return opGreater(left.get(0).listChildrenByName("value"), right.get(0).listChildrenByName("value"), expr);
      } else {
        if (worker.getUcumService() == null) {
          return makeBoolean(false);
        } else {
          var lq = makeQuantity(left.get(0));
          var rq = makeQuantity(right.get(0));
          List<Base> dl = new ArrayList<Base>();
          dl.add(qtyToCanonicalDecimal(lq));
          List<Base> dr = new ArrayList<Base>();
          dr.add(qtyToCanonicalDecimal(rq));
          return opGreater(dl, dr, expr);
        }
      }
    }
    return new ArrayList<Base>();
  }

  private List<Base> opLessOrEqual(List<Base> left, List<Base> right, ExpressionNode expr) throws FHIRException {
    if (left.size() == 0 || right.size() == 0) { 
      return new ArrayList<Base>();
    }
    if (left.size() == 1 && right.size() == 1 && left.get(0).isPrimitive() && right.get(0).isPrimitive()) {
      Base l = left.get(0);
      Base r = right.get(0);
      if (l.hasType(FHIR_TYPES_STRING) && r.hasType(FHIR_TYPES_STRING)) { 
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) <= 0);
      } else if ((l.hasType("integer", "decimal", "unsignedInt", "positiveInt")) && (r.hasType("integer", "decimal", "unsignedInt", "positiveInt"))) { 
        return makeBoolean(new Double(l.primitiveValue()) <= new Double(r.primitiveValue()));
      } else if ((l.hasType("date", "dateTime", "instant")) && (r.hasType("date", "dateTime", "instant"))) {
        Integer i = compareDateTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i <= 0);
        }
      } else if ((l.hasType("time")) && (r.hasType("time"))) {
        Integer i = compareTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i <= 0);
        }
      } else {
        throw makeException(expr, I18nConstants.FHIRPATH_CANT_COMPARE, l.fhirType(), r.fhirType());
      }
    } else if (left.size() == 1 && right.size() == 1 && left.get(0).fhirType().equals("Quantity") && right.get(0).fhirType().equals("Quantity") ) {
      List<Base> lUnits = left.get(0).listChildrenByName("unit");
      String lunit = lUnits.size() == 1 ? lUnits.get(0).primitiveValue() : null;
      List<Base> rUnits = right.get(0).listChildrenByName("unit");
      String runit = rUnits.size() == 1 ? rUnits.get(0).primitiveValue() : null;
      if ((lunit == null && runit == null) || lunit.equals(runit)) {
        return opLessOrEqual(left.get(0).listChildrenByName("value"), right.get(0).listChildrenByName("value"), expr);
      } else {
        if (worker.getUcumService() == null) {
          return makeBoolean(false);
        } else {
          var lq = makeQuantity(left.get(0));
          var rq = makeQuantity(right.get(0));
          List<Base> dl = new ArrayList<Base>();
          dl.add(qtyToCanonicalDecimal(lq));
          List<Base> dr = new ArrayList<Base>();
          dr.add(qtyToCanonicalDecimal(rq));
          return opLessOrEqual(dl, dr, expr);
        }
      }
    }
    return new ArrayList<Base>();
  }

  private List<Base> opGreaterOrEqual(List<Base> left, List<Base> right, ExpressionNode expr) throws FHIRException {
    if (left.size() == 0 || right.size() == 0) { 
      return new ArrayList<Base>();
    }
    if (left.size() == 1 && right.size() == 1 && left.get(0).isPrimitive() && right.get(0).isPrimitive()) {
      Base l = left.get(0);
      Base r = right.get(0);
      if (l.hasType(FHIR_TYPES_STRING) && r.hasType(FHIR_TYPES_STRING)) { 
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) >= 0);
      } else if ((l.hasType("integer", "decimal", "unsignedInt", "positiveInt")) && (r.hasType("integer", "decimal", "unsignedInt", "positiveInt"))) { 
        return makeBoolean(new Double(l.primitiveValue()) >= new Double(r.primitiveValue()));
      } else if ((l.hasType("date", "dateTime", "instant")) && (r.hasType("date", "dateTime", "instant"))) {
        Integer i = compareDateTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i >= 0);
        }
      } else if ((l.hasType("time")) && (r.hasType("time"))) {
        Integer i = compareTimeElements(l, r, false);
        if (i == null) {
          return makeNull();
        } else {
          return makeBoolean(i >= 0);
        }
      } else {
        throw makeException(expr, I18nConstants.FHIRPATH_CANT_COMPARE, l.fhirType(), r.fhirType());
      }
    } else if (left.size() == 1 && right.size() == 1 && left.get(0).fhirType().equals("Quantity") && right.get(0).fhirType().equals("Quantity") ) {
      List<Base> lUnit = left.get(0).listChildrenByName("unit");
      List<Base> rUnit = right.get(0).listChildrenByName("unit");
      if (Base.compareDeep(lUnit, rUnit, true)) {
        return opGreaterOrEqual(left.get(0).listChildrenByName("value"), right.get(0).listChildrenByName("value"), expr);
      } else {
        if (worker.getUcumService() == null) {
          return makeBoolean(false);
        } else {
          var lq = makeQuantity(left.get(0));
          var rq = makeQuantity(right.get(0));
          List<Base> dl = new ArrayList<Base>();
          dl.add(qtyToCanonicalDecimal(lq));
          List<Base> dr = new ArrayList<Base>();
          dr.add(qtyToCanonicalDecimal(rq));
          return opGreaterOrEqual(dl, dr, expr);
        }
      }
    }
    return new ArrayList<Base>();
  }

  private List<Base> opMemberOf(ExecutionContext context, List<Base> left, List<Base> right, ExpressionNode expr) throws FHIRException {
    boolean ans = false;
    String url = right.get(0).primitiveValue();
    ValueSet vs = hostServices != null ? hostServices.resolveValueSet(this, context.appInfo, url) : worker.findTxResource(ValueSet.class, url);
    if (vs != null) {
      for (Base l : left) {
        if (Utilities.existsInList(l.fhirType(), "code", "string", "uri")) {
          if (worker.validateCode(terminologyServiceOptions.withGuessSystem() , TypeConvertor.castToCoding(l), vs).isOk()) {
            ans = true;
          }
        } else if (l.fhirType().equals("Coding")) {
          if (worker.validateCode(terminologyServiceOptions, TypeConvertor.castToCoding(l), vs).isOk()) {
            ans = true;
          }
        } else if (l.fhirType().equals("CodeableConcept")) {
          CodeableConcept cc = TypeConvertor.castToCodeableConcept(l);
          ValidationResult vr = worker.validateCode(terminologyServiceOptions, cc, vs);
          if (vr.isOk()) {
            ans = true;
          }
        } else {
         // DO NOTHING
        }
      }
    }
    return makeBoolean(ans);
  }

  private List<Base> opIn(List<Base> left, List<Base> right, ExpressionNode expr) throws FHIRException {
    if (left.size() == 0) { 
      return new ArrayList<Base>();
    }
    if (right.size() == 0) { 
      return makeBoolean(false);
    }
    if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "in", convertToString(left));
    }
    boolean ans = true;
    for (Base l : left) {
      boolean f = false;
      for (Base r : right) {
        Boolean eq = doEquals(l, r);
        if (eq != null && eq == true) {
          f = true;
          break;
        }
      }
      if (!f) {
        ans = false;
        break;
      }
    }
    return makeBoolean(ans);
  }

  private List<Base> opContains(List<Base> left, List<Base> right, ExpressionNode expr) {
    if (right.size() == 0) { 
      return new ArrayList<Base>();
    }
    if (left.size() == 0) { 
      return makeBoolean(false);
    }
    boolean ans = true;
    for (Base r : right) {
      boolean f = false;
      for (Base l : left) {
        Boolean eq = doEquals(l, r);
        if (eq != null && eq == true) {
          f = true;
          break;
        }
      }
      if (!f) {
        ans = false;
        break;
      }
    }
    return makeBoolean(ans);
  }

  private List<Base> opPlus(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() == 0 || right.size() == 0) { 
      return new ArrayList<Base>();
    }
    if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "+", convertToString(left));
    }
    if (!left.get(0).isPrimitive()) {
      throw makeException(expr, I18nConstants.FHIRPATH_LEFT_VALUE_WRONG_TYPE, "+", left.get(0).fhirType());
    }
    if (right.size() > 1) {
      throw makeExceptionPlural(right.size(), expr, I18nConstants.FHIRPATH_RIGHT_VALUE, "+");
    }
    if (!right.get(0).isPrimitive() &&  !((left.get(0).isDateTime() || left.get(0).hasType("date", "dateTime", "instant", "time") || "0".equals(left.get(0).primitiveValue()) || left.get(0).hasType("Quantity")) && right.get(0).hasType("Quantity"))) {
      throw makeException(expr, I18nConstants.FHIRPATH_RIGHT_VALUE_WRONG_TYPE, "+", right.get(0).fhirType());
    }

    List<Base> result = new ArrayList<Base>();
    Base l = left.get(0);
    Base r = right.get(0);
    if (l.hasType(FHIR_TYPES_STRING) && r.hasType(FHIR_TYPES_STRING)) { 
      result.add(new StringType(l.primitiveValue() + r.primitiveValue()));
    } else if (l.hasType("integer") && r.hasType("integer")) { 
      result.add(new IntegerType(Integer.parseInt(l.primitiveValue()) + Integer.parseInt(r.primitiveValue())));
    } else if (l.hasType("decimal", "integer") && r.hasType("decimal", "integer")) { 
      result.add(new DecimalType(new BigDecimal(l.primitiveValue()).add(new BigDecimal(r.primitiveValue()))));
    } else if (l.hasType("date") && r.hasType("Quantity")) {
      DateType dl = l instanceof DateType ? (DateType) l : new DateType(l.primitiveValue()); 
      var rq = makeQuantity(r);
      result.add(dateAdd(dl, rq, false, expr));
    } else if ((l.isDateTime() || l.hasType("dateTime") || l.hasType("instant")) && r.hasType("Quantity")) {
      DateTimeType dl = l instanceof DateTimeType ? (DateTimeType) l : new DateTimeType(l.primitiveValue()); 
      var rq = makeQuantity(r);
      result.add(dateAdd(dl, rq, false, expr));
    } else if (l.hasType("time") && r.hasType("Quantity")) {
      TimeType dl = l instanceof TimeType ? (TimeType) l : new TimeType(l.primitiveValue()); 
      var rq = makeQuantity(r);
      var rdt = timeAdd(dl, rq, false, expr);
      result.add(rdt); // we only want the time part
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_OP_INCOMPATIBLE, "+", left.get(0).fhirType(), right.get(0).fhirType());
    }
    return result;
  }

  private BaseDateTimeType dateAdd(BaseDateTimeType d, Quantity q, boolean negate, ExpressionNode holder) {
    BaseDateTimeType result = (BaseDateTimeType) d.copy();

    int value = negate ? 0 - q.getValue().intValue() : q.getValue().intValue();
    switch (q.hasCode() ? q.getCode() : q.getUnit()) {
    case "years": 
    case "year": 
      result.add(Calendar.YEAR, value);
      break;
    case "a":
      throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_ARITHMETIC_QTY, q.getCode()), I18nConstants.FHIRPATH_ARITHMETIC_QTY, holder.getOpStart(), holder.toString());
    case "months": 
    case "month": 
      result.add(Calendar.MONTH, value);
      break;
    case "mo":
      throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_ARITHMETIC_QTY, q.getCode()), I18nConstants.FHIRPATH_ARITHMETIC_QTY, holder.getOpStart(), holder.toString());
    case "weeks": 
    case "week": 
    case "wk":
      result.add(Calendar.DAY_OF_MONTH, value * 7);
      break;
    case "days": 
    case "day": 
    case "d":
      result.add(Calendar.DAY_OF_MONTH, value);
      break;
    case "hours": 
    case "hour": 
    case "h":
      result.add(Calendar.HOUR, value);
      break;
    case "minutes": 
    case "minute": 
    case "min":
      result.add(Calendar.MINUTE, value);
      break;
    case "seconds": 
    case "second": 
    case "s":
      result.add(Calendar.SECOND, value);
      double decValue = negate ? 0 - q.getValue().doubleValue() : q.getValue().doubleValue();
      decValue = decValue - value; // remove the integer part, so we can add it in milliseconds
      int ms = (int) (decValue * 1000);
      if (ms != 0) {
        result.add(Calendar.MILLISECOND, ms);
      }
      break;
    case "milliseconds": 
    case "millisecond": 
    case "ms": 
      result.add(Calendar.MILLISECOND, value);
      break;
    default:
      throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_ARITHMETIC_UNIT, q.getCode()), I18nConstants.FHIRPATH_ARITHMETIC_UNIT, holder.getOpStart(), holder.toString());
    }
    return result;
  }

private TimeType timeAdd(TimeType d, Quantity q, boolean negate, ExpressionNode holder) {
    TimeType result = (TimeType) d.copy();

    int value = negate ? 0 - q.getValue().intValue() : q.getValue().intValue();
    switch (q.hasCode() ? q.getCode() : q.getUnit()) {
    case "hours": 
    case "hour": 
    case "h":
      result.add(Calendar.HOUR, value);
      break;
    case "minutes": 
    case "minute": 
    case "min":
      result.add(Calendar.MINUTE, value);
      break;
    case "seconds": 
    case "second": 
    case "s":
      result.add(Calendar.SECOND, value);
      double decValue = negate ? 0 - q.getValue().doubleValue() : q.getValue().doubleValue();
      decValue = decValue - value; // remove the integer part, so we can add it in milliseconds
      int ms = (int) (decValue * 1000);
      if (ms != 0) {
        result.add(Calendar.MILLISECOND, ms);
      }
      break;
    case "milliseconds": 
    case "millisecond": 
    case "ms": 
      result.add(Calendar.MILLISECOND, value);
      break;
    default:
      throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_ARITHMETIC_UNIT, q.getCode()), I18nConstants.FHIRPATH_ARITHMETIC_UNIT, holder.getOpStart(), holder.toString());
    }
    return result;
  }

  private List<Base> opTimes(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() == 0 || right.size() == 0) {
      return new ArrayList<Base>();
    }
    if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "*", convertToString(left));
    }
    var lq = makeQuantity(left.get(0));
    if (!left.get(0).isPrimitive() && !(lq instanceof Quantity)) {
      throw makeException(expr, I18nConstants.FHIRPATH_LEFT_VALUE_WRONG_TYPE, "*", left.get(0).fhirType());
    }
    var rq = makeQuantity(right.get(0));
    if (right.size() > 1) {
      throw makeExceptionPlural(right.size(), expr, I18nConstants.FHIRPATH_RIGHT_VALUE, "*");
    }
    if (!right.get(0).isPrimitive() && !(rq instanceof Quantity)) {
      throw makeException(expr, I18nConstants.FHIRPATH_RIGHT_VALUE_WRONG_TYPE, "*", right.get(0).fhirType());
    }

    List<Base> result = new ArrayList<Base>();
    Base l = left.get(0);
    Base r = right.get(0);

    if (l.hasType("integer") && r.hasType("integer")) { 
      result.add(new IntegerType(Integer.parseInt(l.primitiveValue()) * Integer.parseInt(r.primitiveValue())));
    } else if (l.hasType("decimal", "integer") && r.hasType("decimal", "integer")) { 
      result.add(new DecimalType(new BigDecimal(l.primitiveValue()).multiply(new BigDecimal(r.primitiveValue()))));
    } else if (lq instanceof Quantity && rq instanceof Quantity && worker.getUcumService() != null) {
      Pair pl = qtyToPair(lq);
      Pair pr = qtyToPair(rq);
      Pair p;
      try {
        p = worker.getUcumService().multiply(pl, pr);
        result.add(pairToQty(p));
      } catch (UcumException e) {
        throw new PathEngineException(e.getMessage(), null, expr.getOpStart(), expr.toString(), e); // #TODO: i18n
      }
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_OP_INCOMPATIBLE, "*", left.get(0).fhirType(), right.get(0).fhirType());
    }
    return result;
  }


  private List<Base> opConcatenate(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "&", convertToString(left));
    }
    if (left.size() > 0 && !left.get(0).hasType(FHIR_TYPES_STRING)) {
      throw makeException(expr, I18nConstants.FHIRPATH_LEFT_VALUE_WRONG_TYPE, "&", left.get(0).fhirType());
    }
    if (right.size() > 1) {
      throw makeExceptionPlural(right.size(), expr, I18nConstants.FHIRPATH_RIGHT_VALUE, "&");
    }
    if (right.size() > 0 && !right.get(0).hasType(FHIR_TYPES_STRING)) {
      throw makeException(expr, I18nConstants.FHIRPATH_RIGHT_VALUE_WRONG_TYPE, "&", right.get(0).fhirType());
    }

    List<Base> result = new ArrayList<Base>();
    String l = left.size() == 0 ? "" : left.get(0).primitiveValue();
    String r = right.size() == 0 ? "" : right.get(0).primitiveValue();
    result.add(new StringType(l + r));
    return result;
  }

  private List<Base> opUnion(List<Base> left, List<Base> right, ExpressionNode expr) {
    List<Base> result = new ArrayList<Base>();
    for (Base item : left) {
      if (!doContains(result, item)) {
        result.add(item);
      }
    }
    for (Base item : right) {
      if (!doContains(result, item)) {
        result.add(item);
      }
    }
    return result;
  }

  private boolean doContains(List<Base> list, Base item) {
    for (Base test : list) {
      Boolean eq = doEquals(test, item);
      if (eq != null && eq == true) {
        return true;
      }
    }
    return false;
  }


  private List<Base> opAnd(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    Equality l = asBool(left, expr);
    Equality r = asBool(right, expr);
    switch (l) {
    case False: return makeBoolean(false);
    case Null:
      if (r == Equality.False) {
        return makeBoolean(false);
      } else {
        return makeNull();
      }
    case True:
      switch (r) {
      case False: return makeBoolean(false);
      case Null: return makeNull();
      case True: return makeBoolean(true);
      }
    }
    return makeNull();
  }

  private boolean isBoolean(List<Base> list, boolean b) {
    return list.size() == 1 && list.get(0) instanceof BooleanType && ((BooleanType) list.get(0)).booleanValue() == b;
  }

  private List<Base> opOr(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    Equality l = asBool(left, expr);
    Equality r = asBool(right, expr);
    switch (l) {
    case True: return makeBoolean(true);
    case Null:
      if (r == Equality.True) {
        return makeBoolean(true);
      } else {
        return makeNull();
      }
    case False:
      switch (r) {
      case False: return makeBoolean(false);
      case Null: return makeNull();
      case True: return makeBoolean(true);
      }
    }
    return makeNull();
  }

  private List<Base> opXor(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    Equality l = asBool(left, expr);
    Equality r = asBool(right, expr);
    switch (l) {
    case True: 
      switch (r) {
      case False: return makeBoolean(true);
      case True: return makeBoolean(false);
      case Null: return makeNull();
      }
    case Null:
      return makeNull();
    case False:
      switch (r) {
      case False: return makeBoolean(false);
      case True: return makeBoolean(true);
      case Null: return makeNull();
      }
    }
    return makeNull();
  }

  private List<Base> opImplies(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    Equality eq = asBool(left, expr);
    if (eq == Equality.False) { 
      return makeBoolean(true);
    } else if (right.size() == 0) {
      return makeNull();
    } else switch (asBool(right, expr)) {
    case False: return eq == Equality.Null ? makeNull() : makeBoolean(false);
    case Null: return makeNull();
    case True: return makeBoolean(true);
    }
    return makeNull();
  }


  private List<Base> opMinus(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() == 0 || right.size() == 0) { 
      return new ArrayList<Base>();
    }
    if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "-", convertToString(left));
    }
    if (!left.get(0).isPrimitive() && !left.get(0).hasType("Quantity")) {
      throw makeException(expr, I18nConstants.FHIRPATH_LEFT_VALUE_WRONG_TYPE, "-", left.get(0).fhirType());
    }
    if (right.size() > 1) {
      throw makeExceptionPlural(right.size(), expr, I18nConstants.FHIRPATH_RIGHT_VALUE, "-");
    }
    if (!right.get(0).isPrimitive() &&  !((left.get(0).isDateTime() || left.get(0).hasType("date", "dateTime", "instant", "time") || "0".equals(left.get(0).primitiveValue()) || left.get(0).hasType("Quantity")) && right.get(0).hasType("Quantity"))) {
      throw makeException(expr, I18nConstants.FHIRPATH_RIGHT_VALUE_WRONG_TYPE, "-", right.get(0).fhirType());
    }

    List<Base> result = new ArrayList<Base>();
    Base l = left.get(0);
    Base r = right.get(0);

    if (l.hasType("integer") && r.hasType("integer")) { 
      result.add(new IntegerType(Integer.parseInt(l.primitiveValue()) - Integer.parseInt(r.primitiveValue())));
    } else if (l.hasType("decimal", "integer") && r.hasType("decimal", "integer")) { 
      result.add(new DecimalType(new BigDecimal(l.primitiveValue()).subtract(new BigDecimal(r.primitiveValue()))));
    } else if (l.hasType("decimal", "integer", "Quantity") && r.hasType("Quantity")) { 
      String s = l.primitiveValue();
      if ("0".equals(s)) {
        Quantity qty = makeQuantity(r);
        result.add(qty.copy().setValue(qty.getValue().abs()));
      }
    } else if (l.hasType("date") && r.hasType("Quantity")) {
      DateType dl = l instanceof DateType ? (DateType) l : new DateType(l.primitiveValue()); 
      result.add(dateAdd(dl, makeQuantity(r), true, expr));
    } else if ((l.isDateTime() || l.hasType("dateTime") || l.hasType("instant")) && r.hasType("Quantity")) {
      DateTimeType dl = l instanceof DateTimeType ? (DateTimeType) l : new DateTimeType(l.primitiveValue()); 
      result.add(dateAdd(dl, makeQuantity(r), true, expr));
    } else if (l.hasType("time") && r.hasType("Quantity")) {
      TimeType dl = l instanceof TimeType ? (TimeType) l : new TimeType(l.primitiveValue()); 
      var rdt = timeAdd(dl, makeQuantity(r), true, expr);
      result.add(rdt); // we only want the time part
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_OP_INCOMPATIBLE, "-", left.get(0).fhirType(), right.get(0).fhirType());
    }
    return result;
  }

  private List<Base> opDivideBy(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() == 0 || right.size() == 0) {
      return new ArrayList<Base>();
    }
    if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "/", convertToString(left));
    }
    var lq = makeQuantity(left.get(0));
    if (!left.get(0).isPrimitive() && !(lq instanceof Quantity)) {
      throw makeException(expr, I18nConstants.FHIRPATH_LEFT_VALUE_WRONG_TYPE, "/", left.get(0).fhirType());
    }
    if (right.size() > 1) {
      throw makeExceptionPlural(right.size(), expr, I18nConstants.FHIRPATH_RIGHT_VALUE, "/");
    }
    var rq = makeQuantity(right.get(0));
    if (!right.get(0).isPrimitive() && !(rq instanceof Quantity)) {
      throw makeException(expr, I18nConstants.FHIRPATH_RIGHT_VALUE_WRONG_TYPE, "/", right.get(0).fhirType());
    }

    List<Base> result = new ArrayList<Base>();
    Base l = left.get(0);
    Base r = right.get(0);

    if (l.hasType("integer", "decimal", "unsignedInt", "positiveInt") && r.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      Decimal d1;
      try {
        d1 = new Decimal(l.primitiveValue());
        Decimal d2 = new Decimal(r.primitiveValue());
        result.add(new DecimalType(d1.divide(d2).asDecimal()));
      } catch (UcumException e) {
        // just return nothing
      }
    } else if (lq instanceof Quantity && rq instanceof Quantity && worker.getUcumService() != null) {
      Pair pl = qtyToPair(lq);
      Pair pr = qtyToPair(rq);
      Pair p;
      try {
        p = worker.getUcumService().divideBy(pl, pr);
        result.add(pairToQty(p));
      } catch (UcumException e) {
        // just return nothing
      }
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_OP_INCOMPATIBLE, "/", left.get(0).fhirType(), right.get(0).fhirType());
    }
    return result;
  }

  private List<Base> opDiv(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() == 0 || right.size() == 0) { 
      return new ArrayList<Base>();
    }
    if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "div", convertToString(left));
    }
    if (!left.get(0).isPrimitive()) {
      throw makeException(expr, I18nConstants.FHIRPATH_LEFT_VALUE_WRONG_TYPE, "div", left.get(0).fhirType());
    }
    if (right.size() > 1) {
      throw makeExceptionPlural(right.size(), expr, I18nConstants.FHIRPATH_RIGHT_VALUE, "div");
    }
    if (!right.get(0).isPrimitive()) {
      throw makeException(expr, I18nConstants.FHIRPATH_RIGHT_VALUE_WRONG_TYPE, "div", right.get(0).fhirType());
    }

    List<Base> result = new ArrayList<Base>();
    Base l = left.get(0);
    Base r = right.get(0);

    if (l.hasType("integer") && r.hasType("integer")) {
      int divisor = Integer.parseInt(r.primitiveValue());
      if (divisor != 0) { 
        result.add(new IntegerType(Integer.parseInt(l.primitiveValue()) / divisor));
      }
    } else if (l.hasType("decimal", "integer") && r.hasType("decimal", "integer")) { 
      Decimal d1;
      try {
        d1 = new Decimal(l.primitiveValue());
        Decimal d2 = new Decimal(r.primitiveValue());
        result.add(new IntegerType(d1.divInt(d2).asDecimal()));
      } catch (UcumException e) {
        // just return nothing
      }
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_OP_INCOMPATIBLE, "div", left.get(0).fhirType(), right.get(0).fhirType());
    }
    return result;
  }

  private List<Base> opMod(List<Base> left, List<Base> right, ExpressionNode expr) throws PathEngineException {
    if (left.size() == 0 || right.size() == 0) {
      return new ArrayList<Base>();
    } if (left.size() > 1) {
      throw makeExceptionPlural(left.size(), expr, I18nConstants.FHIRPATH_LEFT_VALUE, "mod", convertToString(left));
    }
    if (!left.get(0).isPrimitive()) {
      throw makeException(expr, I18nConstants.FHIRPATH_LEFT_VALUE_WRONG_TYPE, "mod", left.get(0).fhirType());
    }
    if (right.size() > 1) {
      throw makeExceptionPlural(right.size(), expr, I18nConstants.FHIRPATH_RIGHT_VALUE, "mod");
    }
    if (!right.get(0).isPrimitive()) {
      throw makeException(expr, I18nConstants.FHIRPATH_RIGHT_VALUE_WRONG_TYPE, "mod", right.get(0).fhirType());
    }

    List<Base> result = new ArrayList<Base>();
    Base l = left.get(0);
    Base r = right.get(0);

    if (l.hasType("integer") && r.hasType("integer")) { 
      int modulus = Integer.parseInt(r.primitiveValue());
      if (modulus != 0) {
        result.add(new IntegerType(Integer.parseInt(l.primitiveValue()) % modulus));
      }
    } else if (l.hasType("decimal", "integer") && r.hasType("decimal", "integer")) {
      Decimal d1;
      try {
        d1 = new Decimal(l.primitiveValue());
        Decimal d2 = new Decimal(r.primitiveValue());
        result.add(new DecimalType(d1.modulo(d2).asDecimal()));
      } catch (UcumException e) {
        throw new PathEngineException(e);
      }
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_OP_INCOMPATIBLE, "mod", left.get(0).fhirType(), right.get(0).fhirType());
    }
    return result;
  }


  private TypeDetails resolveConstantType(ExecutionTypeContext context, Base constant, ExpressionNode expr, FHIRPathConstantEvaluationMode mode) throws PathEngineException {
    if (constant instanceof BooleanType) { 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    } else if (constant instanceof IntegerType) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer);
    } else if (constant instanceof DecimalType) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Decimal);
    } else if (constant instanceof FHIRConstant) {
      return resolveConstantType(context, ((FHIRConstant) constant).getValue(), expr, mode);
    } else if (constant == null) {
      return new TypeDetails(CollectionStatus.SINGLETON);      
    } else 
    {
      var q = makeQuantity(constant);
      if (q instanceof Quantity) {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Quantity);
      } else {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
      }
    }
  }

  private TypeDetails resolveConstantType(ExecutionTypeContext context, String s, ExpressionNode expr, FHIRPathConstantEvaluationMode mode) throws PathEngineException {
    if (s.startsWith("@")) {
      if (s.startsWith("@T")) {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Time);
      } else {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_DateTime);
      }
    } else if (s.equals("%sct")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (s.equals("%loinc")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (s.equals("%ucum")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (s.equals("%resource")) {
      if (context.resource == null) {
        throw makeException(expr, I18nConstants.FHIRPATH_CANNOT_USE, "%resource", "no focus resource");
      }
      return new TypeDetails(CollectionStatus.SINGLETON, context.resource);
    } else if (s.equals("%rootResource")) {
      if (context.rootResource == null) {
        throw makeException(expr, I18nConstants.FHIRPATH_CANNOT_USE, "%rootResource", "no focus rootResource");
      }
      return new TypeDetails(CollectionStatus.SINGLETON, context.rootResource);
    } else if (s.equals("%context")) {
      return context.context;
    } else if (s.equals("%map-codes")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (s.equals("%us-zip")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (s.startsWith("%`vs-")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (s.startsWith("%`cs-")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (s.startsWith("%`ext-")) {
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    } else if (hostServices == null) {
      String varName = s.substring(1);
      if (context.hasDefinedVariable(varName))
        return context.getDefinedVariable(varName);
      throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONSTANT, s);
    } else {
      String varName = s.substring(1);
      if (context.hasDefinedVariable(varName))
        return context.getDefinedVariable(varName);
      TypeDetails v = hostServices.resolveConstantType(this, context.appInfo, mode == FHIRPathConstantEvaluationMode.EXPLICIT ? s.substring(1) : s, mode);
      if (v == null) {
        throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_CONSTANT, s); 
      } else {
        return v;
      }
    }
  }

  private List<Base> execute(ExecutionContext context, Base item, ExpressionNode exp, boolean atEntry) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (atEntry && context.appInfo != null && hostServices != null && checkWithHostServicesBeforeHand) {
      // we'll see if the name matches a constant known by the context.
      List<Base> temp = hostServices.resolveConstant(this, context.appInfo, exp.getName(), FHIRPathConstantEvaluationMode.IMPLICIT_BEFORE);
      if (!temp.isEmpty()) {
        result.addAll(temp);
        return result;
      }
    }
    if (atEntry && exp.getName() != null && Character.isUpperCase(exp.getName().charAt(0))) {// special case for start up
      StructureDefinition sd = worker.fetchTypeDefinition(item.fhirType());
      if (sd == null) {
        // logical model
        if (exp.getName().equals(item.fhirType())) {
          result.add(item);          
        }
      } else {
        while (sd != null) {
          if (sd.getType().equals(exp.getName()) || sd.getTypeTail().equals(exp.getName())) {  
            result.add(item);
            break;
          }
          sd = worker.fetchResource(StructureDefinition.class, sd.getBaseDefinition(), sd);
        }
      }
    } else {
      getChildrenByName(item, exp.getName(), result);
    }
    if (atEntry && context.appInfo != null && hostServices != null && result.isEmpty()) {
      // well, we didn't get a match on the name - we'll see if the name matches a constant known by the context.
      // (if the name does match, and the user wants to get the constant value, they'll have to try harder...
      result.addAll(hostServices.resolveConstant(this, context.appInfo, exp.getName(), FHIRPathConstantEvaluationMode.IMPLICIT_AFTER));
    }
    return result;
  }     

  private String getParent(String rn) {
    return null;
  }


  private TypeDetails executeContextType(ExecutionTypeContext context, String name, ExpressionNode expr, FHIRPathConstantEvaluationMode mode) throws PathEngineException, DefinitionException {
    if (hostServices == null) {
      throw makeException(expr, I18nConstants.FHIRPATH_HO_HOST_SERVICES, "Context Reference");
    }
    return hostServices.resolveConstantType(this, context.appInfo, name, mode);
  }

  private TypeDetails executeType(String type, ExpressionNode exp, boolean atEntry, TypeDetails focus, Set<ElementDefinition> elementDependencies) throws PathEngineException, DefinitionException {
    if (atEntry && Character.isUpperCase(exp.getName().charAt(0)) && (hashTail(type).equals(exp.getName()) || isAncestor(type, exp.getName()) )) { // special case for start up
      return new TypeDetails(CollectionStatus.SINGLETON, type);
    }
    TypeDetails result = new TypeDetails(focus.getCollectionStatus());
    getChildTypesByName(type, exp.getName(), result, exp, focus, elementDependencies);
    return result;
  }


  private boolean isAncestor(String wanted, String stated) {
    try {
      StructureDefinition sd = worker.fetchTypeDefinition(wanted);
      while (sd != null) {
        if (stated.equals(sd.getTypeName())) {
          return true;
        }
        sd = worker.fetchResource(StructureDefinition.class, sd.getBaseDefinition());
      }
      return false;
    } catch (Exception e) { 
      return false;
    }
  }

  private String hashTail(String type) {
    return type.contains("#") ? "" : type.substring(type.lastIndexOf("/")+1);
  }


  private void evaluateParameters(ExecutionTypeContext context, TypeDetails focus, ExpressionNode exp, Set<ElementDefinition> elementDependencies, List<TypeDetails> paramTypes, boolean canBeNone) {
    int i = 0;
    for (ExpressionNode exprParam : exp.getParameters()) {
      if (isExpressionParameter(exp, i)) {
        paramTypes.add(executeType(changeThis(context, focus), focus, exprParam, elementDependencies, true, canBeNone, exp));
      } else {
        paramTypes.add(executeType(context, focus, exprParam, elementDependencies, true, canBeNone, exp));
      }
      i++;
    }
  }

  @SuppressWarnings("unchecked")
  private TypeDetails evaluateFunctionType(ExecutionTypeContext context, TypeDetails focus, ExpressionNode exp, Set<ElementDefinition> elementDependencies,  ExpressionNode container) throws PathEngineException, DefinitionException {
    List<TypeDetails> paramTypes = new ArrayList<TypeDetails>();
    if (exp.getFunction() == Function.Is || exp.getFunction() == Function.As || exp.getFunction() == Function.OfType || (exp.getFunction() == Function.Custom && hostServices.paramIsType(exp.getName(), 0))) {
      paramTypes.add(new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String));
    } else if (exp.getFunction() == Function.Repeat && exp.getParameters().size() == 1) {
      TypeDetails base = TypeDetails.empty();
      TypeDetails lFocus = focus;
      boolean changed = false;
      do {
        evaluateParameters(context, lFocus, exp, elementDependencies, paramTypes, true);
        changed = false;
        if (!base.contains(paramTypes.get(0))) {
          changed = true;
          base.addTypes(paramTypes.get(0));
          lFocus = base;
        }
      } while (changed);
      paramTypes.clear();
      paramTypes.add(base);
    } else if (exp.getFunction() == Function.Where || exp.getFunction() == Function.Select || exp.getFunction() == Function.Exists || 
        exp.getFunction() == Function.All || exp.getFunction() == Function.AllTrue || exp.getFunction() == Function.AnyTrue 
        || exp.getFunction() == Function.AllFalse || exp.getFunction() == Function.AnyFalse) {
      evaluateParameters(context, focus.toSingleton(), exp, elementDependencies, paramTypes, false);
    } else {
      evaluateParameters(context, focus, exp, elementDependencies, paramTypes, false);
    }
    if (exp.getFunction() == Function.First || exp.getFunction() == Function.Last || exp.getFunction() == Function.Tail || exp.getFunction() == Function.Skip || exp.getFunction() == Function.Take) {
      if (focus.getCollectionStatus() == CollectionStatus.SINGLETON) {
        typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_NOT_A_COLLECTION, container.toString()), I18nConstants.FHIRPATH_NOT_A_COLLECTION));

      }
    }
    switch (exp.getFunction()) {
    case Empty : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Not : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Exists : { 
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    }
    case SubsetOf : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, focus.toUnordered()); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean); 
    }
    case SupersetOf : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, focus); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean); 
    }
    case IsDistinct : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Distinct : 
      return focus;
    case Count : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer);
    case Where : 
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean)); 
      // special case: where the focus is Reference, and the parameter to where is resolve() "is", we will suck up the target types
      if (focus.hasType("Reference")) {
        boolean canRestrictTargets = !exp.getParameters().isEmpty();
        List<String> targets = new ArrayList<>();
        if (canRestrictTargets) {
          ExpressionNode p = exp.getParameters().get(0);
          if (p.getKind() == Kind.Function && p.getName().equals("resolve") && p.getOperation() == Operation.Is) {
            targets.add(p.getOpNext().getName());
          } else {
            canRestrictTargets = false;
          }
        }
        if (canRestrictTargets) {
          TypeDetails td = focus.copy();
          td.getTargets().clear();
          td.getTargets().addAll(targets);
          return td;
        } else {
          return focus;
        }
      } else {
        return focus;
      }
    case Select : 
      return paramTypes.get(0);
    case All : 
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Repeat : 
      return paramTypes.get(0); 
    case Aggregate : 
      return anything(focus.getCollectionStatus());
    case Item : {
      checkOrdered(focus, "item", exp);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer)); 
      return focus.toSingleton(); 
    }
    case As : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String));
      String tn = checkType(focus, exp);
      TypeDetails td = new TypeDetails(CollectionStatus.SINGLETON, tn);
      if (td.typesHaveTargets()) {
        td.addTargets(focus.getTargets());
      }
      return td;
    }
    case OfType : { 
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String));
      String tn = checkType(focus, exp);
      TypeDetails td = new TypeDetails(CollectionStatus.SINGLETON, tn);
      if (td.typesHaveTargets()) {
        td.addTargets(focus.getTargets());
      }
      return td;
    }
    case Type : { 
      boolean s = false;
      boolean c = false;
      for (ProfiledType pt : focus.getProfiledTypes()) {
        s = s || pt.isSystemType();
        c = c || !pt.isSystemType();
      }
      if (s && c) {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_SimpleTypeInfo, TypeDetails.FP_ClassInfo);
      } else if (s) {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_SimpleTypeInfo);
      } else {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_ClassInfo);
      }
    }
    case Is : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean); 
    }
    case Single :
      return focus.toSingleton();
    case First : {
      checkOrdered(focus, "first", exp);
      return focus.toSingleton();
    }
    case Last : {
      checkOrdered(focus, "last", exp);
      return focus.toSingleton();
    }
    case Tail : {
      checkOrdered(focus, "tail", exp);
      return focus;
    }
    case Skip : {
      checkOrdered(focus, "skip", exp);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer)); 
      return focus;
    }
    case Take : {
      checkOrdered(focus, "take", exp);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer)); 
      return focus;
    }
    case Union : {
      return focus.union(paramTypes.get(0));
    }
    case Combine : {
      return focus.union(paramTypes.get(0));
    }
    case Intersect : {
      return focus.intersect(paramTypes.get(0));
    }
    case Exclude : {
      return focus;
    }
    case Iif : {
      TypeDetails types = new TypeDetails(null);
      checkSingleton(focus, "iif", exp);       
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean));       
      types.update(paramTypes.get(1));
      if (paramTypes.size() > 2) {
        types.update(paramTypes.get(2));
      }
      return types;
    }
    case Lower : {
      checkContextString(focus, "lower", exp, true);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String); 
    }
    case Upper : {
      checkContextString(focus, "upper", exp, true);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String); 
    }
    case ToChars : {
      checkContextString(focus, "toChars", exp, true);
      return new TypeDetails(CollectionStatus.ORDERED, TypeDetails.FP_String); 
    }
    case IndexOf : {
      checkContextString(focus, "indexOf", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer); 
    }
    case Substring : {
      checkContextString(focus, "subString", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer), new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String); 
    }
    case StartsWith : {
      checkContextString(focus, "startsWith", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean); 
    }
    case EndsWith : {
      checkContextString(focus, "endsWith", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean); 
    }
    case Matches : {
      checkContextString(focus, "matches", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean); 
    }
    case MatchesFull : {
      checkContextString(focus, "matches", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean); 
    }
    case ReplaceMatches : {
      checkContextString(focus, "replaceMatches", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String), new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String); 
    }
    case Contains : {
      checkContextString(focus, "contains", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    }
    case Replace : {
      checkContextString(focus, "replace", exp, true);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String), new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    }
    case Length : { 
      checkContextPrimitive(focus, "length", false, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer);
    }
    case Children : 
      return childTypes(focus, "*", exp);
    case Descendants : 
      return childTypes(focus, "**", exp);
    case MemberOf : {
      checkContextCoded(focus, "memberOf", exp);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    }
    case Trace : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return focus; 
    }
    case DefineVariable : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.UNORDERED, TypeDetails.FP_String)); 
      // set the type of the variable
      // Actually evaluate the value of the first parameter (to get the name of the variable if possible)
      // and if have that, set it into the context
      ExpressionNode p = exp.getParameters().get(0);
      if (p.getKind() == Kind.Constant && p.getConstant() != null) {
        String varName = exp.getParameters().get(0).getConstant().primitiveValue();
        if (varName != null) {
          if (paramTypes.size() > 1)
            context.setDefinedVariable(varName, paramTypes.get(1));
          else
            context.setDefinedVariable(varName, focus);
        }
      } else {
        // this variable is not a constant, so we can't analyze what name it could have
      }
      return focus; 
    }
    case Check : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return focus; 
    }
    case Today : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_DateTime);
    case Now : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_DateTime);
    case Resolve : {
      checkContextReference(focus, "resolve", exp);
      return new TypeDetails(focus.getCollectionStatus(), "Resource"); 
    }
    case Extension : {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String));
      ExpressionNode p = exp.getParameters().get(0);
      if (p.getKind() == Kind.Constant && p.getConstant() != null) {
        String url = exp.getParameters().get(0).getConstant().primitiveValue();
        if (!Utilities.isAbsoluteUrl(url) && focus.hasType("Extension")) {
          TypeDetails res = new TypeDetails(CollectionStatus.ORDERED);
          List<String> profiles = focus.getProfiles("Extension");
          if (profiles != null) {
            for (String pt : profiles) {
              String extn = pt.contains("#") ? pt.substring(0, pt.indexOf("#")) : pt;
              String subExtn = pt.contains("#") ? pt.substring(0, pt.indexOf("#")) : null;
              StructureDefinition sd = worker.fetchResource(StructureDefinition.class, extn);
              if (sd != null) {
                String id = subExtn == null ? "Extension.extension:"+url : subExtn+".extension:"+url;
                ElementDefinition ed = sd.getSnapshot().getElementById(id);
                if (ed != null) {
                  res.addType("Extension", sd.getUrl()+"#"+id);
                }
              }
            }
          }
          if (res.isEmpty()) {
            typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_UNKNOWN_EXTENSION, url), I18nConstants.FHIRPATH_UNKNOWN_EXTENSION));            
          } else {
            return res;
          }
        } else {
          ExtensionDefinition ed = findExtensionDefinition(focus, url);
          if (ed != null) {
            return new TypeDetails(CollectionStatus.ORDERED, new ProfiledType(ed.sd.getUrl()));
          } else {
            typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_UNKNOWN_EXTENSION, url), I18nConstants.FHIRPATH_UNKNOWN_EXTENSION));
          }
        }
        return new TypeDetails(CollectionStatus.SINGLETON, "Extension");
      }
    }
    case AnyTrue: 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case AllTrue: 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case AnyFalse: 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case AllFalse: 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case HasValue : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case HtmlChecks1 : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case HtmlChecks2 : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Comparable : 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    case Encode:
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    case Decode:
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    case Escape:
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    case Unescape:
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    case Trim:
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    case Split:
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    case Join:
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    case ToInteger : {
      checkContextPrimitive(focus, "toInteger", true, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer);
    }
    case ToDecimal : {
      checkContextPrimitive(focus, "toDecimal", true, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Decimal);
    }
    case ToString : {
      checkContextPrimitive(focus, "toString", true, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String);
    }
    case ToQuantity : {
      checkContextPrimitive(focus, "toQuantity", true, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Quantity);
    }
    case ToBoolean : {
      checkContextPrimitive(focus, "toBoolean", false, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    }
    case ToDateTime : {
      checkContextPrimitive(focus, "ToDateTime", false, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_DateTime);
    }
    case ToTime : {
      checkContextPrimitive(focus, "ToTime", false, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Time);
    }
    case ConvertsToString : 
    case ConvertsToQuantity :{
      checkContextPrimitive(focus, exp.getFunction().toCode(), true, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    } 
    case ConvertsToInteger : 
    case ConvertsToDecimal : 
    case ConvertsToDateTime : 
    case ConvertsToDate : 
    case ConvertsToTime : 
    case ConvertsToBoolean : {
      checkContextPrimitive(focus, exp.getFunction().toCode(), false, exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    }
    case ConformsTo: {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);       
    }
    case Abs : {
      checkContextNumerical(focus, "abs", exp);
      return new TypeDetails(CollectionStatus.SINGLETON, focus.getTypes());       
    }
    case Sort :
      return new TypeDetails(CollectionStatus.ORDERED, focus.getTypes());       
    case Coalesce : {
      TypeDetails types = new TypeDetails(null);
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes);
      for (var t : paramTypes) {
        types.update(t);
      }
      return types;
    }
    case Truncate :
    case Floor : 
    case Ceiling : {
      checkContextDecimal(focus, exp.getFunction().toCode(), exp);
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer);       
    }  

    case Round :{
      checkContextDecimal(focus, "round", exp);
      if (paramTypes.size() > 0) {
        checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer));
      }
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Decimal);       
    } 

    case Exp : 
    case Ln : 
    case Sqrt : {
      checkContextNumerical(focus, exp.getFunction().toCode(), exp);      
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Decimal);       
    }
    case Log :  {
      checkContextNumerical(focus, exp.getFunction().toCode(), exp);      
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_NUMBERS));
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Decimal);       
    }
    case Power : {
      checkContextNumerical(focus, exp.getFunction().toCode(), exp);      
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_NUMBERS));
      return new TypeDetails(CollectionStatus.SINGLETON, focus.getTypes());       
    }

    case LowBoundary:
    case HighBoundary: {
      checkContextContinuous(focus, exp.getFunction().toCode(), exp, true);      
      if (paramTypes.size() > 0) {
        checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer));
      }
      if ((focus.hasType("date") || focus.hasType("datetime") || focus.hasType("instant"))) {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Decimal, TypeDetails.FP_DateTime);       
      } else if ((focus.hasType("time"))) {
          return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Time, TypeDetails.FP_Time);       
      } else if (focus.hasType("decimal") || focus.hasType("integer")) {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Decimal);       
      } else {
        return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_DateTime);       
      }
    }
    case Precision: {
      checkContextContinuous(focus, exp.getFunction().toCode(), exp, false);      
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Integer);       
    }
    case hasTemplateIdOf: {
      checkParamTypes(exp, exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_String)); 
      return new TypeDetails(CollectionStatus.SINGLETON, TypeDetails.FP_Boolean);
    }
    case Custom : {
      return hostServices.checkFunction(this, context.appInfo,exp.getName(), focus, paramTypes);
    }
    default:
      break;
    }
    throw new Error("not Implemented yet");
  }

  private ExtensionDefinition findExtensionDefinition(TypeDetails focus, String url) {
    if (Utilities.isAbsoluteUrl(url)) {
      StructureDefinition sd = worker.fetchResource(StructureDefinition.class, url);
      if (sd == null) {
        return null;
      } else {
        return new ExtensionDefinition(true, sd, sd.getSnapshot().getElementFirstRep());
      }
    }
    StructureDefinition sd = worker.fetchResource(StructureDefinition.class, focus.getType());
    if (sd != null) {
      for (ElementDefinition ed : sd.getSnapshot().getElement()) {
        if (ed.hasFixed() && url.equals(ed.getFixed().primitiveValue())) {
          return new ExtensionDefinition(false, sd, ed);
        }
      }
    }
    return null;
  }

  private String checkType(TypeDetails focus, ExpressionNode exp) {
    String tn;
    if (exp.getParameters().get(0).getInner() != null) {
      tn = exp.getParameters().get(0).getName()+"."+exp.getParameters().get(0).getInner().getName();
    } else {
      tn = "FHIR."+exp.getParameters().get(0).getName();
    }
    if (tn.startsWith("System.")) {
      tn = tn.substring(7);
    } else if (tn.startsWith("FHIR.")) {
      tn = Utilities.pathURL(Constants.NS_FHIR_ROOT, "StructureDefinition", tn.substring(5));
    } else if (tn.startsWith("CDA.")) {
      tn = Utilities.pathURL(Constants.NS_CDA_ROOT, "StructureDefinition", tn.substring(4));
    }
    
    if (typeCastIsImpossible(focus, tn)) {
      typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_OFTYPE_IMPOSSIBLE, focus.describeMin(), tn, exp.toString()), I18nConstants.FHIRPATH_OFTYPE_IMPOSSIBLE));
    }
    return tn;
  }

  private boolean typeCastIsImpossible(TypeDetails focus, String tn) {
    for (ProfiledType pt : focus.getProfiledTypes()) {
      if (!pt.hasProfiles()) { // get back to this later
        String purl = tn;
        while (purl != null && !purl.equals(pt.getUri())) {
          StructureDefinition sd = worker.fetchResource(StructureDefinition.class, purl);
          purl = sd == null ? null : sd.getBaseDefinition();
        }
        if (purl != null) {
          return false;
        }
      }
    }
    return !focus.hasType(tn);
  }

  private boolean isExpressionParameter(ExpressionNode exp, int i) {
    if (exp.getFunction() == Function.Sort) {
      return true;
    }
    
    switch (i) {
    case 0:
      return exp.getFunction() == Function.Where || exp.getFunction() == Function.Exists || exp.getFunction() == Function.All || exp.getFunction() == Function.Select || exp.getFunction() == Function.Repeat || exp.getFunction() == Function.Aggregate;
    case 1:
      return exp.getFunction() == Function.Trace || exp.getFunction() == Function.DefineVariable;
    default: 
      return false;
    }
  }


  private void checkParamTypes(ExpressionNode expr, String funcName,List<TypeDetails> paramTypes, TypeDetails... typeSet) throws PathEngineException {
    int i = 0;
    for (TypeDetails pt : typeSet) {
      if (i == paramTypes.size()) {
        return;
      }
      TypeDetails actual = paramTypes.get(i);
      i++;
      for (String a : actual.getTypes()) {
        if (!pt.hasType(worker, a)) {
          throw makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, funcName, i, a, pt.toString());
        }
      }
      if (actual.getCollectionStatus() != CollectionStatus.SINGLETON && pt.getCollectionStatus() == CollectionStatus.SINGLETON) {
        typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_COLLECTION_STATUS_PARAMETER, funcName, i, expr.toString()), I18nConstants.FHIRPATH_COLLECTION_STATUS_PARAMETER));
      }
    }
  }

  private void checkSingleton(TypeDetails focus, String name, ExpressionNode expr) throws PathEngineException {
    if (focus.getCollectionStatus() != CollectionStatus.SINGLETON) {
      typeWarnings.add(new IssueMessage(worker.formatMessage(I18nConstants.FHIRPATH_COLLECTION_STATUS_CONTEXT, name, expr.toString()), I18nConstants.FHIRPATH_COLLECTION_STATUS_CONTEXT));
    }
  }

  private void checkOrdered(TypeDetails focus, String name, ExpressionNode expr) throws PathEngineException {
    if (focus.getCollectionStatus() == CollectionStatus.UNORDERED) {
      throw makeException(expr, I18nConstants.FHIRPATH_ORDERED_ONLY, name);
    }
  }

  private void checkContextReference(TypeDetails focus, String name, ExpressionNode expr) throws PathEngineException {
    if (!focus.hasType(worker, "string") && !focus.hasType(worker, "uri") && !focus.hasType(worker, "url") && !focus.hasType(worker, "Reference") && !focus.hasType(worker, "canonical")) {
      throw makeException(expr, I18nConstants.FHIRPATH_REFERENCE_ONLY, name, focus.describe());
    }
  }


  private void checkContextCoded(TypeDetails focus, String name, ExpressionNode expr) throws PathEngineException {
    if (!focus.hasType(worker, "string") && !focus.hasType(worker, "code") && !focus.hasType(worker, "uri") && !focus.hasType(worker, "Coding") && !focus.hasType(worker, "CodeableConcept")) {
      throw makeException(expr, I18nConstants.FHIRPATH_CODED_ONLY, name, focus.describe());
    }
  }


  private void checkContextString(TypeDetails focus, String name, ExpressionNode expr, boolean sing) throws PathEngineException {
    if (!focus.hasNoTypes() && !focus.hasType(worker, "string") && !focus.hasType(worker, "code") && !focus.hasType(worker, "uri") && !focus.hasType(worker, "url") && !focus.hasType(worker, "canonical") && !focus.hasType(worker, "id")) {
      throw makeException(expr, sing ? I18nConstants.FHIRPATH_STRING_SING_ONLY : I18nConstants.FHIRPATH_STRING_ORD_ONLY, name, focus.describe());
    }
  }


  private void checkContextPrimitive(TypeDetails focus, String name, boolean canQty, ExpressionNode expr) throws PathEngineException {
    if (!focus.hasNoTypes()) {
      if (canQty) {
        if (!focus.hasType(primitiveTypes) && !focus.hasType("Quantity")) {
          throw makeException(expr, I18nConstants.FHIRPATH_PRIMITIVE_ONLY, name, focus.describe(), "Quantity, "+primitiveTypes.toString());
        }
      } else if (!focus.hasType(primitiveTypes)) {
        throw makeException(expr, I18nConstants.FHIRPATH_PRIMITIVE_ONLY, name, focus.describe(), primitiveTypes.toString());
      }
    }
  }

  private void checkContextNumerical(TypeDetails focus, String name, ExpressionNode expr) throws PathEngineException {
    if (!focus.hasNoTypes() && !focus.hasType("integer")  && !focus.hasType("decimal") && !focus.hasType("Quantity")) {
      throw makeException(expr, I18nConstants.FHIRPATH_NUMERICAL_ONLY, name, focus.describe());
    }    
  }

  private void checkContextDecimal(TypeDetails focus, String name, ExpressionNode expr) throws PathEngineException {
    if (!focus.hasNoTypes() && !focus.hasType("decimal") && !focus.hasType("integer")) {
      throw makeException(expr, I18nConstants.FHIRPATH_DECIMAL_ONLY, name, focus.describe());
    }    
  }

  private void checkContextContinuous(TypeDetails focus, String name, ExpressionNode expr, boolean allowInteger) throws PathEngineException {
    if (!focus.hasNoTypes() && !focus.hasType("decimal") && !focus.hasType("date") && !focus.hasType("dateTime") && !focus.hasType("time") && !focus.hasType("Quantity") && !(allowInteger && focus.hasType("integer"))) {
      throw makeException(expr, I18nConstants.FHIRPATH_CONTINUOUS_ONLY, name, focus.describe());
    }    
  }

  private TypeDetails childTypes(TypeDetails focus, String mask, ExpressionNode expr) throws PathEngineException, DefinitionException {
    TypeDetails result = new TypeDetails(CollectionStatus.UNORDERED);
    for (String f : focus.getTypes()) {
      getChildTypesByName(f, mask, result, expr, null, null);
    }
    return result;
  }

  private TypeDetails anything(CollectionStatus status) {
    return new TypeDetails(status, allTypes.keySet());
  }

  //    private boolean isPrimitiveType(String s) {
  //            return s.equals("boolean") || s.equals("integer") || s.equals("decimal") || s.equals("base64Binary") || s.equals("instant") || s.equals("string") || s.equals("uri") || s.equals("date") || s.equals("dateTime") || s.equals("time") || s.equals("code") || s.equals("oid") || s.equals("id") || s.equals("unsignedInt") || s.equals("positiveInt") || s.equals("markdown");
  //    }

  private List<Base> evaluateFunction(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    switch (exp.getFunction()) {
    case Empty : return funcEmpty(context, focus, exp);
    case Not : return funcNot(context, focus, exp);
    case Exists : return funcExists(context, focus, exp);
    case SubsetOf : return funcSubsetOf(context, focus, exp);
    case SupersetOf : return funcSupersetOf(context, focus, exp);
    case IsDistinct : return funcIsDistinct(context, focus, exp);
    case Distinct : return funcDistinct(context, focus, exp);
    case Count : return funcCount(context, focus, exp);
    case Where : return funcWhere(context, focus, exp);
    case Select : return funcSelect(context, focus, exp);
    case All : return funcAll(context, focus, exp);
    case Repeat : return funcRepeat(context, focus, exp);
    case Aggregate : return funcAggregate(context, focus, exp);
    case Item : return funcItem(context, focus, exp);
    case As : return funcAs(context, focus, exp);
    case OfType : return funcOfType(context, focus, exp);
    case Type : return funcType(context, focus, exp);
    case Is : return funcIs(context, focus, exp);
    case Single : return funcSingle(context, focus, exp);
    case First : return funcFirst(context, focus, exp);
    case Last : return funcLast(context, focus, exp);
    case Tail : return funcTail(context, focus, exp);
    case Skip : return funcSkip(context, focus, exp);
    case Take : return funcTake(context, focus, exp);
    case Union : return funcUnion(context, focus, exp);
    case Combine : return funcCombine(context, focus, exp);
    case Intersect : return funcIntersect(context, focus, exp);
    case Exclude : return funcExclude(context, focus, exp);
    case Iif : return funcIif(context, focus, exp);
    case Lower : return funcLower(context, focus, exp);
    case Upper : return funcUpper(context, focus, exp);
    case ToChars : return funcToChars(context, focus, exp);
    case IndexOf : return funcIndexOf(context, focus, exp);
    case Substring : return funcSubstring(context, focus, exp);
    case StartsWith : return funcStartsWith(context, focus, exp);
    case EndsWith : return funcEndsWith(context, focus, exp);
    case Matches : return funcMatches(context, focus, exp);
    case MatchesFull : return funcMatchesFull(context, focus, exp);
    case ReplaceMatches : return funcReplaceMatches(context, focus, exp);
    case Contains : return funcContains(context, focus, exp);
    case Replace : return funcReplace(context, focus, exp);
    case Length : return funcLength(context, focus, exp);
    case Children : return funcChildren(context, focus, exp);
    case Descendants : return funcDescendants(context, focus, exp);
    case MemberOf : return funcMemberOf(context, focus, exp);
    case Trace : return funcTrace(context, focus, exp);
    case DefineVariable : return funcDefineVariable(context, focus, exp);
    case Check : return funcCheck(context, focus, exp);
    case Today : return funcToday(context, focus, exp);
    case Now : return funcNow(context, focus, exp);
    case Resolve : return funcResolve(context, focus, exp);
    case Extension : return funcExtension(context, focus, exp);
    case AnyFalse: return funcAnyFalse(context, focus, exp);
    case AllFalse: return funcAllFalse(context, focus, exp);
    case AnyTrue: return funcAnyTrue(context, focus, exp);
    case AllTrue: return funcAllTrue(context, focus, exp);
    case HasValue : return funcHasValue(context, focus, exp);
    case Encode : return funcEncode(context, focus, exp);
    case Decode : return funcDecode(context, focus, exp);
    case Escape : return funcEscape(context, focus, exp);
    case Unescape : return funcUnescape(context, focus, exp);
    case Trim : return funcTrim(context, focus, exp);
    case Split : return funcSplit(context, focus, exp);
    case Join : return funcJoin(context, focus, exp); 
    case HtmlChecks1 : return funcHtmlChecks1(context, focus, exp);
    case HtmlChecks2 : return funcHtmlChecks2(context, focus, exp);
    case Comparable : return funcComparable(context, focus, exp);
    case ToInteger : return funcToInteger(context, focus, exp);
    case ToDecimal : return funcToDecimal(context, focus, exp);
    case ToString : return funcToString(context, focus, exp);
    case ToBoolean : return funcToBoolean(context, focus, exp);
    case ToQuantity : return funcToQuantity(context, focus, exp);
    case ToDateTime : return funcToDateTime(context, focus, exp);
    case ToTime : return funcToTime(context, focus, exp);
    case ConvertsToInteger : return funcIsInteger(context, focus, exp);
    case ConvertsToDecimal : return funcIsDecimal(context, focus, exp);
    case ConvertsToString : return funcIsString(context, focus, exp);
    case ConvertsToBoolean : return funcIsBoolean(context, focus, exp);
    case ConvertsToQuantity : return funcIsQuantity(context, focus, exp);
    case ConvertsToDateTime : return funcIsDateTime(context, focus, exp);
    case ConvertsToDate : return funcIsDate(context, focus, exp);
    case ConvertsToTime : return funcIsTime(context, focus, exp);
    case ConformsTo : return funcConformsTo(context, focus, exp);
    case Round : return funcRound(context, focus, exp); 
    case Sqrt : return funcSqrt(context, focus, exp); 
    case Abs : return funcAbs(context, focus, exp); 
    case Ceiling : return funcCeiling(context, focus, exp); 
    case Exp : return funcExp(context, focus, exp); 
    case Floor : return funcFloor(context, focus, exp); 
    case Ln : return funcLn(context, focus, exp); 
    case Log : return funcLog(context, focus, exp); 
    case Power : return funcPower(context, focus, exp); 
    case Truncate : return funcTruncate(context, focus, exp);
    case Sort : return funcSort(context, focus, exp);
    case Coalesce: return funcCoalesce(context, focus, exp);
    case LowBoundary : return funcLowBoundary(context, focus, exp);
    case HighBoundary : return funcHighBoundary(context, focus, exp);
    case Precision : return funcPrecision(context, focus, exp);
    case hasTemplateIdOf: return funcHasTemplateIdOf(context, focus, exp);


    case Custom: { 
      List<List<Base>> params = new ArrayList<List<Base>>();
      if (hostServices.paramIsType( exp.getName(), 0)) {
        if (exp.getParameters().size() > 0) {
          String tn;
          if (exp.getParameters().get(0).getInner() != null) {
            tn = exp.getParameters().get(0).getName()+"."+exp.getParameters().get(0).getInner().getName();
          } else {
            tn = "FHIR."+exp.getParameters().get(0).getName();
          }
          List<Base> p = new ArrayList<>();
          p.add(new CodeType(tn));
          params.add(p);
        }
      } else {
        for (ExpressionNode p : exp.getParameters()) {
          params.add(execute(context, focus, p, true));
        }
      }
      return hostServices.executeFunction(this, context.appInfo, focus, exp.getName(), params);
    }
    default:
      throw new Error("not Implemented yet");
    }
  }

  private List<Base> funcHasTemplateIdOf(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    List<Base> swb = execute(context, focus, exp.getParameters().get(0), true);
    String sw = convertToString(swb);

    StructureDefinition sd = this.worker.fetchResource(StructureDefinition.class, sw);
    if (focus.size() == 1 && sd != null) {
      boolean found = false;
      for (Identifier id : sd.getIdentifier()) {
        if (id.getValue().startsWith("urn:hl7ii:")) {   
          String[] p = id.getValue().split("\\:");
          if (p.length == 4) {
            found = found || hasTemplateId(focus.get(0), p[2], p[3]);
          }
        } else if (id.getValue().startsWith("urn:oid:")) {
          found = found || hasTemplateId(focus.get(0), id.getValue().substring(8));          
        }
      }
      result.add(new BooleanType(found));
    }
    return result;
  }

  private boolean hasTemplateId(Base base, String rv) {
    List<Base> templateIds = base.listChildrenByName("templateId");
    for (Base templateId : templateIds) {
      Base root = templateId.getChildValueByName("root");
      Base extension = templateId.getChildValueByName("extension");
      if (extension == null && root != null && rv.equals(root.primitiveValue())) {
        return true;
      }
    }    
    return false;
  }

  private boolean hasTemplateId(Base base, String rv, String ev) {
    List<Base> templateIds = base.listChildrenByName("templateId");
    for (Base templateId : templateIds) {
      Base root = templateId.getChildValueByName("root");
      Base extension = templateId.getChildValueByName("extension");
      if (extension != null && ev.equals(extension.primitiveValue()) && root != null && rv.equals(root.primitiveValue())) {
        return true;
      }
    }    
    return false;
  }
  
  private List<Base> funcSqrt(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "sqrt", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      Double d = Double.parseDouble(base.primitiveValue());
      try {
        result.add(new DecimalType(Math.sqrt(d)));
      } catch (Exception e) {
        // just return nothing
      }
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "sqrt", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }


  private List<Base> funcAbs(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "abs", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      Double d = Double.parseDouble(base.primitiveValue());
      try {
        result.add(new DecimalType(Math.abs(d)));
      } catch (Exception e) {
        // just return nothing
      }
    } else if (base.hasType("Quantity")) {
      Quantity qty = makeQuantity(base);
      result.add(qty.copy().setValue(qty.getValue().abs()));
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "abs", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }


  private List<Base> funcCeiling(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "ceiling", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      Double d = Double.parseDouble(base.primitiveValue());
      try {result.add(new IntegerType((int) Math.ceil(d)));
      } catch (Exception e) {
        // just return nothing
      }
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "ceiling", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }

  private List<Base> funcFloor(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "floor", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      Double d = Double.parseDouble(base.primitiveValue());
      try {
        result.add(new IntegerType((int) Math.floor(d)));
      } catch (Exception e) {
        // just return nothing
      }
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "floor", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }


  private List<Base> funcExp(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() > 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "exp", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      Double d = Double.parseDouble(base.primitiveValue());
      try {
        result.add(new DecimalType(Math.exp(d)));
      } catch (Exception e) {
        // just return nothing
      }

    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "exp", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;  
  }


  private List<Base> funcLn(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "ln", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      Double d = Double.parseDouble(base.primitiveValue());
      try {
        result.add(new DecimalType(Math.log(d)));
      } catch (Exception e) {
        // just return nothing
      }        
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "ln", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }


  private List<Base> funcLog(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "log", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      List<Base> n1 = execute(context, focus, expr.getParameters().get(0), true);
      if (n1.size() == 0) {
        // no base, so we just return nothing (as per the spec)
        return new ArrayList<Base>();
      }
      if (n1.size() != 1) {
        throw makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "log", "0", "Multiple Values", "integer or decimal");
      }
      Double e = Double.parseDouble(n1.get(0).primitiveValue());
      Double d = Double.parseDouble(base.primitiveValue());
      try {
        result.add(new DecimalType(customLog(e, d)));
      } catch (Exception ex) {
        // just return nothing
      }
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "log", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }

  private static double customLog(double base, double logNumber) {
    return Math.log(logNumber) / Math.log(base);
  }

  private List<Base> funcPower(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "power", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      List<Base> n1 = execute(context, focus, expr.getParameters().get(0), true);
      if (n1.size() == 0) {
        // no base, so we just return nothing (as per the spec)
        return new ArrayList<Base>();
      }
      if (n1.size() != 1) {
        throw makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "power", "0", "Multiple Values", "integer or decimal");
      }
      Double e = Double.parseDouble(n1.get(0).primitiveValue());
      Double d = Double.parseDouble(base.primitiveValue());
      try {
        result.add(new DecimalType(Math.pow(d, e)));
      } catch (Exception ex) {
        // just return nothing
      }
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "power", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }

  private List<Base> funcTruncate(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "truncate", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      String s = base.primitiveValue();
      if (s.contains(".")) {
        s = s.substring(0, s.indexOf("."));
      }
      result.add(new IntegerType(s));
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "sqrt", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }

  private List<Base> funcLowBoundary(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return makeNull();
    }
    if (focus.size() > 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "lowBoundary", focus.size());
    }
    Integer precision = null;
    if (expr.getParameters().size() > 0) {
      List<Base> n1 = execute(context, focus, expr.getParameters().get(0), true);
      if (n1.size() != 1) {
        throw makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "lowBoundary", "0", "Multiple Values", "integer");
      }
      precision = Integer.parseInt(n1.get(0).primitiveValue());
    }
    
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    
    if (base.hasType("decimal")) {
      if (precision == null || (precision >= 0 && precision < 17)) {
        result.add(new DecimalType(Utilities.lowBoundaryForDecimal(base.primitiveValue(), precision == null ? 8 : precision)));
      }
    } else if (base.hasType("integer")) {
      if (precision == null || (precision >= 0 && precision < 17)) {
        result.add(new DecimalType(Utilities.lowBoundaryForDecimal(base.primitiveValue(), precision == null ? 8 : precision)));
      }
    } else if (base.hasType("date")) {
      result.add(new DateTimeType(DateTimeUtil.lowBoundaryForDate(base.primitiveValue(), precision == null ? 10 : precision)));
    } else if (base.hasType("dateTime")) {
      result.add(new DateTimeType(DateTimeUtil.lowBoundaryForDate(base.primitiveValue(), precision == null ? 17 : precision)));
    } else if (base.hasType("time")) {
      result.add(new TimeType(DateTimeUtil.lowBoundaryForTime(base.primitiveValue(), precision == null ? 9 : precision)));
    } else if (base.hasType("Quantity")) {
      String value = getNamedValue(base, "value");
      Base v = base.copy();
      v.setProperty("value", new DecimalType(Utilities.lowBoundaryForDecimal(value, precision == null ? 8 : precision)));
      result.add(v);
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "sqrt", "(focus)", base.fhirType(), "decimal or date");
    }
    return result;
  }
  
  private List<Base> funcHighBoundary(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return makeNull();
    }
    if (focus.size() > 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "highBoundary", focus.size());
    }
    Integer precision = null;
    if (expr.getParameters().size() > 0) {
      List<Base> n1 = execute(context, focus, expr.getParameters().get(0), true);
      if (n1.size() != 1) {
        throw makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "lowBoundary", "0", "Multiple Values", "integer");
      }
      precision = Integer.parseInt(n1.get(0).primitiveValue());
    }
    
    
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("decimal")) {
      if (precision == null || (precision >= 0 && precision < 17)) {
        result.add(new DecimalType(Utilities.highBoundaryForDecimal(base.primitiveValue(), precision == null ? 8 : precision)));
      }
    } else if (base.hasType("integer")) {
      if (precision == null || (precision >= 0 && precision < 17)) {
        result.add(new DecimalType(Utilities.highBoundaryForDecimal(base.primitiveValue(), precision == null ? 8 : precision)));
      }
    } else if (base.hasType("date")) {
      result.add(new DateTimeType(DateTimeUtil.highBoundaryForDate(base.primitiveValue(), precision == null ? 10 : precision)));
    } else if (base.hasType("dateTime")) {
      result.add(new DateTimeType(DateTimeUtil.highBoundaryForDate(base.primitiveValue(), precision == null ? 17 : precision)));
    } else if (base.hasType("time")) {
      result.add(new TimeType(DateTimeUtil.highBoundaryForTime(base.primitiveValue(), precision == null ? 9 : precision)));
    } else if (base.hasType("Quantity")) {
      String value = getNamedValue(base, "value");
      Base v = base.copy();
      v.setProperty("value", new DecimalType(Utilities.highBoundaryForDecimal(value, precision == null ? 8 : precision)));
      result.add(v);
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "sqrt", "(focus)", base.fhirType(), "decimal or date");
    }
    return result;
  }
  
  private List<Base> funcPrecision(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "highBoundary", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("decimal")) {
      result.add(new IntegerType(Utilities.getDecimalPrecision(base.primitiveValue())));
    } else if (base.hasType("date") || base.hasType("dateTime")) {
      result.add(new IntegerType(DateTimeUtil.getDatePrecision(base.primitiveValue())));
    } else if (base.hasType("time")) {
      result.add(new IntegerType(DateTimeUtil.getTimePrecision(base.primitiveValue())));
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "sqrt", "(focus)", base.fhirType(), "decimal or date");
    }
    return result;
  }

  private List<Base> funcRound(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    if (focus.size() == 0) {
      return new ArrayList<Base>();
    }
    if (focus.size() != 1) {
      throw makeExceptionPlural(focus.size(), expr, I18nConstants.FHIRPATH_FOCUS, "round", focus.size());
    }
    Base base = focus.get(0);
    List<Base> result = new ArrayList<Base>();
    if (base.hasType("integer", "decimal", "unsignedInt", "positiveInt")) {
      int i = 0;
      if (expr.getParameters().size() == 1) {
        List<Base> n1 = execute(context, focus, expr.getParameters().get(0), true);
        if (n1.size() != 1) {
          throw makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "power", "0", "Multiple Values", "integer");
        }
        i = Integer.parseInt(n1.get(0).primitiveValue());
      }
      BigDecimal  d = new BigDecimal (base.primitiveValue());
      result.add(new DecimalType(d.setScale(i, RoundingMode.HALF_UP)));
    } else {
      makeException(expr, I18nConstants.FHIRPATH_WRONG_PARAM_TYPE, "round", "(focus)", base.fhirType(), "integer or decimal");
    }
    return result;
  }

  private static final char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
  private ContextUtilities cu;
  public static String bytesToHex(byte[] bytes) {
    char[] hexChars = new char[bytes.length * 2];
    for (int j = 0; j < bytes.length; j++) {
      int v = bytes[j] & 0xFF;
      hexChars[j * 2] = HEX_ARRAY[v >>> 4];
      hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
    }
    return new String(hexChars);
  }

  public static byte[] hexStringToByteArray(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
      data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16));
    }
    return data;
  }

  private List<Base> funcEncode(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String param = nl.get(0).primitiveValue();

    List<Base> result = new ArrayList<Base>();

    if (focus.size() == 1) {
      String cnt = focus.get(0).primitiveValue();
      if ("hex".equals(param)) {
        result.add(new StringType(bytesToHex(cnt.getBytes())));        
      } else if ("base64".equals(param)) {
        Base64.Encoder enc = Base64.getEncoder();
        result.add(new StringType(enc.encodeToString(cnt.getBytes())));
      } else if ("urlbase64".equals(param)) {
        Base64.Encoder enc = Base64.getUrlEncoder();
        result.add(new StringType(enc.encodeToString(cnt.getBytes())));
      }
    }
    return result;      
  }

  private List<Base> funcDecode(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String param = nl.get(0).primitiveValue();

    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      String cnt = focus.get(0).primitiveValue();
      if ("hex".equals(param)) {
        result.add(new StringType(new String(hexStringToByteArray(cnt))));        
      } else if ("base64".equals(param)) {
        Base64.Decoder enc = Base64.getDecoder();
        result.add(new StringType(new String(enc.decode(cnt))));
      } else if ("urlbase64".equals(param)) {
        Base64.Decoder enc = Base64.getUrlDecoder();
        result.add(new StringType(new String(enc.decode(cnt))));
      }
    }
    return result;  
  }

  private List<Base> funcEscape(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String param = nl.get(0).primitiveValue();

    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      String cnt = focus.get(0).primitiveValue();
      if ("html".equals(param)) {
        result.add(new StringType(Utilities.escapeXml(cnt)));        
      } else if ("json".equals(param)) {
        result.add(new StringType(Utilities.escapeJson(cnt)));        
      } else if ("url".equals(param)) {
        result.add(new StringType(Utilities.URLEncode(cnt)));        
      } else if ("md".equals(param)) {
        result.add(new StringType(MarkDownProcessor.makeStringSafeAsMarkdown(cnt)));        
      }
    }

    return result;  
  }

  private List<Base> funcUnescape(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String param = nl.get(0).primitiveValue();

    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      String cnt = focus.get(0).primitiveValue();
      if ("html".equals(param)) {
        result.add(new StringType(Utilities.unescapeXml(cnt)));        
      } else if ("json".equals(param)) {
        result.add(new StringType(Utilities.unescapeJson(cnt)));        
      } else if ("url".equals(param)) {
        result.add(new StringType(Utilities.URLDecode(cnt)));        
      } else if ("md".equals(param)) {
        result.add(new StringType(MarkDownProcessor.makeMarkdownForString(cnt)));        
      }
    }

    return result;  
  }

  private List<Base> funcTrim(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      String cnt = focus.get(0).primitiveValue();
      result.add(new StringType(cnt.trim()));
    }
    return result;  
  }

  private List<Base> funcSplit(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String param = nl.get(0).primitiveValue();

    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      String cnt = focus.get(0).primitiveValue();
      String[] sl = Utilities.simpleSplit(cnt, param);
      for (String s : sl) {
        result.add(new StringType(s));
      }
    }
    return result;  
  }

  private List<Base> funcJoin(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> nl = exp.getParameters().size() > 0 ? execute(context, focus, exp.getParameters().get(0), true) : new ArrayList<Base>();
    String param = "";
    String param2 = "";
    if (exp.getParameters().size() > 0) {
      param = nl.get(0).primitiveValue();
      param2 = param;
      if (exp.getParameters().size() == 2) {
        nl = execute(context, focus, exp.getParameters().get(1), true);
        param2 = nl.get(0).primitiveValue();
      }
    }
    
    List<Base> result = new ArrayList<Base>();
    CommaSeparatedStringBuilder b = new CommaSeparatedStringBuilder(param, param2);
    for (Base i : focus) {
      b.append(i.primitiveValue());    
    }
    result.add(new StringType(b.toString()));
    return result;  
  }

  private List<Base> funcHtmlChecks1(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    // todo: actually check the HTML
    if (focus.size() != 1) {
      return makeBoolean(false);          
    }
    XhtmlNode x = focus.get(0).getXhtml();
    if (x == null) {
      return makeBoolean(false);                
    }
    boolean ok = checkHtmlNames(x, true);
    if (ok && VersionUtilities.isR6Plus(this.worker.getVersion())) {
      ok = checkForContent(x);
    }
    return makeBoolean(ok);    
  }

  private List<Base> funcHtmlChecks2(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    // todo: actually check the HTML
    if (focus.size() != 1) {
      return makeBoolean(false);          
    }
    XhtmlNode x = focus.get(0).getXhtml();
    if (x == null) {
      return makeBoolean(false);                
    }
    return makeBoolean(checkForContent(x));    
  }

  private boolean checkForContent(XhtmlNode x) {
    if ((x.getNodeType() == NodeType.Text && !Utilities.noString(x.getContent().trim())) || (x.getNodeType() == NodeType.Element && "img".equals(x.getName()))) {
      return true;
    }
    for (XhtmlNode c : x.getChildNodes()) {
      if (checkForContent(c)) {
        return true;
      }
    }
    return false;
  }

  private List<Base> funcComparable(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    if (focus.size() != 1 || !(focus.get(0).fhirType().equals("Quantity"))) {
      return makeBoolean(false);          
    }
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    if (nl.size() != 1 || !(nl.get(0).fhirType().equals("Quantity"))) {
      return makeBoolean(false);          
    }
    String s1 = getNamedValue(focus.get(0), "system");
    String u1 = getNamedValue(focus.get(0), "code");
    String s2 = getNamedValue(nl.get(0), "system");
    String u2 = getNamedValue(nl.get(0), "code");
    
    if (s1 == null || s2 == null || !s1.equals(s2)) {
      return makeBoolean(false);                
    }
    if (u1 == null || u2 == null) {
      return makeBoolean(false);                
    }
    if (u1.equals(u2)) {
      return makeBoolean(true);
    }
    if (s1.equals("http://unitsofmeasure.org") && worker.getUcumService() != null) {
      try {
        return makeBoolean(worker.getUcumService().isComparable(u1, u2));
      } catch (UcumException e) {
        return makeBoolean(false);  
      }  
    } else {
      return makeBoolean(false);  
    }
  }


  private String getNamedValue(Base base, String name) {
    Property p = base.getChildByName(name);
    if (p.hasValues() && p.getValues().size() == 1) {
      return p.getValues().get(0).primitiveValue();
    }
    return null;
  }

  private boolean checkHtmlNames(XhtmlNode node, boolean block) {
    if (node.getNodeType() == NodeType.Comment) {
      if (node.getContent().startsWith("DOCTYPE"))
        return false;
    }
    if (node.getNodeType() == NodeType.Element) {
      if (block) {
        if (!Utilities.existsInList(node.getName(),
            "p", "br", "div", "h1", "h2", "h3", "h4", "h5", "h6", "a", "span", "b", "em", "i", "strong",
            "small", "big", "tt", "small", "dfn", "q", "var", "abbr", "acronym", "cite", "blockquote", "hr", "address", "bdo", "kbd", "q", "sub", "sup",
            "ul", "ol", "li", "dl", "dt", "dd", "pre", "table", "caption", "colgroup", "col", "thead", "tr", "tfoot", "tbody", "th", "td",
            "code", "samp", "img", "map", "area")) {
          return false;
        }        
      } else {
        if (!Utilities.existsInList(node.getName(),
            "a", "span", "b", "em", "i", "strong", "small", "big", "small", "q", "var", "abbr", "acronym", "cite", "kbd", "q", "sub", "sup", "code", "samp", "img", "map", "area")) {
          return false;
        }
      }
      for (String an : node.getAttributes().keySet()) {
        boolean ok = an.startsWith("xmlns") || Utilities.existsInList(an,
            "title", "style", "class", "id", "lang", "xml:lang", "xml:space", "dir", "accesskey", "tabindex",
            // tables
            "span", "width", "align", "valign", "char", "charoff", "abbr", "axis", "headers", "scope", "rowspan", "colspan") ||

            Utilities.existsInList(node.getName() + "." + an, "a.href", "a.name", "img.src", "img.border", "div.xmlns", "blockquote.cite", "q.cite",
                "a.charset", "a.type", "a.name", "a.href", "a.hreflang", "a.rel", "a.rev", "a.shape", "a.coords", "img.src",
                "img.alt", "img.longdesc", "img.height", "img.width", "img.usemap", "img.ismap", "map.name", "area.shape",
                "area.coords", "area.href", "area.nohref", "area.alt", "table.summary", "table.width", "table.border",
                "table.frame", "table.rules", "table.cellspacing", "table.cellpadding", "pre.space", "td.nowrap"
                );
        if (!ok) {
          return false;
        }
      }
      for (XhtmlNode c : node.getChildNodes()) {
        if (!checkHtmlNames(c, block && !"p".equals(c))) {
          return false;
        }
      }
    }
    return true;
  }

  private List<Base> funcAll(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (exp.getParameters().size() == 1) {
      List<Base> pc = new ArrayList<Base>();
      boolean all = true;
      for (Base item : focus) {
        pc.clear();
        pc.add(item);
        Equality eq = asBool(execute(changeThis(context, item), pc, exp.getParameters().get(0), true), exp);
        if (eq != Equality.True) {
          all = false;
          break;
        }
      }
      result.add(new BooleanType(all).noExtensions());
    } else {// (exp.getParameters().size() == 0) {
      boolean all = true;
      for (Base item : focus) {
        Equality eq = asBool(item, true);
        if (eq != Equality.True) {
          all = false;
          break;
        }
      }
      result.add(new BooleanType(all).noExtensions());
    }
    return result;
  }


  private ExecutionContext changeThis(ExecutionContext context, Base newThis) {
    ExecutionContext newContext = new ExecutionContext(context.appInfo, context.focusResource, context.rootResource, context.context, newThis);
    // append all of the defined variables from the context into the new context
    if (context.definedVariables != null) {
      for (String s : context.definedVariables.keySet()) {
        newContext.setDefinedVariable(s, context.definedVariables.get(s));
      }
    }
    return newContext;
  }

  private ExecutionContext contextForParameter(ExecutionContext context) {
    ExecutionContext newContext = new ExecutionContext(context.appInfo, context.focusResource, context.rootResource, context.context, context.thisItem);
    newContext.total = context.total;
    newContext.index = context.index;
    // append all of the defined variables from the context into the new context
    if (context.definedVariables != null) {
      for (String s : context.definedVariables.keySet()) {
        newContext.setDefinedVariable(s, context.definedVariables.get(s));
      }
    }
    return newContext;
  }

  private ExecutionTypeContext changeThis(ExecutionTypeContext context, TypeDetails newThis) {
    ExecutionTypeContext newContext = new ExecutionTypeContext(context.appInfo, context.rootResource, context.resource, context.context, newThis);
    // append all of the defined variables from the context into the new context
    if (context.definedVariables != null) {
      for (String s : context.definedVariables.keySet()) {
        newContext.setDefinedVariable(s, context.definedVariables.get(s));
      }
    }
    return newContext;
  }

  private ExecutionTypeContext contextForParameter(ExecutionTypeContext context) {
    ExecutionTypeContext newContext = new ExecutionTypeContext(context.appInfo, context.rootResource, context.resource, context.context, context.thisItem);
    // append all of the defined variables from the context into the new context
    if (context.definedVariables != null) {
      for (String s : context.definedVariables.keySet()) {
        newContext.setDefinedVariable(s, context.definedVariables.get(s));
      }
    }
    return newContext;
  }

  private List<Base> funcNow(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    result.add(DateTimeType.now());
    return result;
  }


  private List<Base> funcToday(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    result.add(new DateType(new Date(), TemporalPrecisionEnum.DAY));
    return result;
  }


  private List<Base> funcMemberOf(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    if (nl.size() != 1 || focus.size() != 1) {
      return new ArrayList<Base>();
    }

    String url = nl.get(0).primitiveValue();
    ValueSet vs = hostServices != null ? hostServices.resolveValueSet(this, context.appInfo, url) : worker.findTxResource(ValueSet.class, url);
    if (vs == null) {
      return new ArrayList<Base>();
    }
    Base l = focus.get(0);
    if (Utilities.existsInList(l.fhirType(), "code", "string", "uri")) {
      return makeBoolean(worker.validateCode(terminologyServiceOptions.withGuessSystem(), TypeConvertor.castToCoding(l), vs).isOk());
    } else if (l.fhirType().equals("Coding")) {
      return makeBoolean(worker.validateCode(terminologyServiceOptions, TypeConvertor.castToCoding(l), vs).isOk());
    } else if (l.fhirType().equals("CodeableConcept")) {
      return makeBoolean(worker.validateCode(terminologyServiceOptions, TypeConvertor.castToCodeableConcept(l), vs).isOk());
    } else {
      return new ArrayList<Base>();
    }
  }


  private List<Base> funcDescendants(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> current = new ArrayList<Base>();
    current.addAll(focus);
    List<Base> added = new ArrayList<Base>();
    boolean more = true;
    while (more) {
      added.clear();
      for (Base item : current) {
        getChildrenByName(item, "*", added);
      }
      more = !added.isEmpty();
      result.addAll(added);
      current.clear();
      current.addAll(added);
    }
    return result;
  }


  private List<Base> funcChildren(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    for (Base b : focus) {
      getChildrenByName(b, "*", result);
    }
    return result;
  }


  private List<Base> funcReplace(ExecutionContext context, List<Base> focus, ExpressionNode expr) throws FHIRException, PathEngineException {
    List<Base> result = new ArrayList<Base>();
    List<Base> tB = execute(context, focus, expr.getParameters().get(0), true);
    String t = convertToString(tB);
    List<Base> rB = execute(context, focus, expr.getParameters().get(1), true);
    String r = convertToString(rB);

    if (focus.size() == 0 || tB.size() == 0 || rB.size() == 0) {
      //
    } else if (focus.size() == 1) {
      if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
        String f = convertToString(focus.get(0));
        if (Utilities.noString(f)) {
          result.add(new StringType(""));
        } else {
          String n = f.replace(t, r);
          result.add(new StringType(n));
        }
      }
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_NO_COLLECTION, "replace", focus.size());
    }
    return result;
  }


  private List<Base> funcReplaceMatches(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> regexB = execute(context, focus, exp.getParameters().get(0), true);
    String regex = convertToString(regexB);
    List<Base> replB = execute(context, focus, exp.getParameters().get(1), true);
    String repl = convertToString(replB);

    if (focus.size() == 0 || regexB.size() == 0 || replB.size() == 0) {
      //
    } else if (focus.size() == 1 && !Utilities.noString(regex)) {
      if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
        result.add(new StringType(convertToString(focus.get(0)).replaceAll(regex, repl)).noExtensions());
      }
    } else {
      result.add(new StringType(convertToString(focus.get(0))).noExtensions());
    }
    return result;
  }


  private List<Base> funcEndsWith(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> swb = execute(context, focus, exp.getParameters().get(0), true);
    String sw = convertToString(swb);

    if (focus.size() == 0) {
      //
    } else if (swb.size() == 0) {
      //
    } else if (Utilities.noString(sw)) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
      if (focus.size() == 1 && !Utilities.noString(sw)) {
        result.add(new BooleanType(convertToString(focus.get(0)).endsWith(sw)).noExtensions());
      } else {
        result.add(new BooleanType(false).noExtensions());
      }
    }
    return result;
  }


  private List<Base> funcToString(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    for (Base item : focus) {
      String value = convertToString(item);
      if (value != null)
        result.add(new StringType(value).noExtensions());
    }

    if (result.size() > 1) {
      throw makeException(exp, I18nConstants.FHIRPATH_NO_COLLECTION, "toString", result.size());
    }
    return result;
  }

  private List<Base> funcToBoolean(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      if (focus.get(0) instanceof BooleanType) {
        result.add(focus.get(0));
      } else if (focus.get(0) instanceof IntegerType) {
        int i = Integer.parseInt(focus.get(0).primitiveValue());
        if (i == 0) {
          result.add(new BooleanType(false).noExtensions());
        } else if (i == 1) {
          result.add(new BooleanType(true).noExtensions());
        }
      } else if (focus.get(0) instanceof DecimalType) {
        if (((DecimalType) focus.get(0)).getValue().compareTo(BigDecimal.ZERO) == 0) {
          result.add(new BooleanType(false).noExtensions());
        } else if (((DecimalType) focus.get(0)).getValue().compareTo(BigDecimal.ONE) == 0) {
          result.add(new BooleanType(true).noExtensions());
        }
      } else if (focus.get(0) instanceof StringType) {
        if ("true".equalsIgnoreCase(focus.get(0).primitiveValue())) {
          result.add(new BooleanType(true).noExtensions());
        } else if ("false".equalsIgnoreCase(focus.get(0).primitiveValue())) {
          result.add(new BooleanType(false).noExtensions()); 
        }
      }
    }
    return result;
  }

  private List<Base> funcToQuantity(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      var qty = makeQuantity(focus.get(0));
      if (qty instanceof Quantity) {
        result.add(qty);
      } else if (focus.get(0) instanceof StringType) {
        Quantity q = parseQuantityString(focus.get(0).primitiveValue());
        if (q != null) {
          result.add(q.noExtensions());
        }
      } else if (focus.get(0) instanceof IntegerType) {
        result.add(new Quantity().setValue(new BigDecimal(focus.get(0).primitiveValue())).setSystem("http://unitsofmeasure.org").setCode("1").noExtensions());
      } else if (focus.get(0) instanceof DecimalType) {
        result.add(new Quantity().setValue(new BigDecimal(focus.get(0).primitiveValue())).setSystem("http://unitsofmeasure.org").setCode("1").noExtensions());
      }
    }
    return result;
  }

  private List<Base> funcToDateTime(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    //  List<Base> result = new ArrayList<Base>();
    //  result.add(new BooleanType(convertToBoolean(focus)));
    //  return result;
    throw makeException(expr, I18nConstants.FHIRPATH_NOT_IMPLEMENTED, "toDateTime");
  }

  private List<Base> funcToTime(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    //  List<Base> result = new ArrayList<Base>();
    //  result.add(new BooleanType(convertToBoolean(focus)));
    //  return result;
    throw makeException(expr, I18nConstants.FHIRPATH_NOT_IMPLEMENTED, "toTime");
  }


  private List<Base> funcToDecimal(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    String s = convertToString(focus);
    List<Base> result = new ArrayList<Base>();
    if (Utilities.isDecimal(s, true)) {
      result.add(new DecimalType(s).noExtensions());
    }
    if ("true".equals(s)) {
      result.add(new DecimalType(1).noExtensions());
    }
    if ("false".equals(s)) {
      result.add(new DecimalType(0).noExtensions());
    }
    return result;
  }


  private List<Base> funcIif(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    if (focus.size() > 1) {
      throw makeException(exp, I18nConstants.FHIRPATH_NO_COLLECTION, "iif", focus.size());    
    }
    
    List<Base> n1 = execute(focus.isEmpty() ? context : changeThis(context, focus.get(0)), focus, exp.getParameters().get(0), true);
    Equality v = asBool(n1, exp);
    if (v == Equality.True) {
      return execute(context, focus, exp.getParameters().get(1), true);
    } else if (exp.getParameters().size() < 3) {
      return new ArrayList<Base>();
    } else {
      return execute(context, focus, exp.getParameters().get(2), true);
    }
  }


  private List<Base> funcTake(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> n1 = execute(context, focus, exp.getParameters().get(0), true);
    int i1 = Integer.parseInt(n1.get(0).primitiveValue());

    List<Base> result = new ArrayList<Base>();
    for (int i = 0; i < Math.min(focus.size(), i1); i++) {
      result.add(focus.get(i));
    }
    return result;
  }


  private List<Base> funcUnion(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    for (Base item : focus) {
      if (!doContains(result, item)) {
        result.add(item);
      }
    }
    for (Base item : execute(context, focus, exp.getParameters().get(0), true)) {
      if (!doContains(result, item)) {
        result.add(item);
      }
    }
    return result;
  }

  private List<Base> funcCombine(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    for (Base item : focus) {
      result.add(item);
    }
    for (Base item : execute(context, focus, exp.getParameters().get(0), true)) {
      result.add(item);
    }
    return result;
  }

  private List<Base> funcIntersect(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> other = execute(context, focus, exp.getParameters().get(0), true);

    for (Base item : focus) {
      if (!doContains(result, item) && doContains(other, item)) {
        result.add(item);
      }
    }
    return result;    
  }

  private List<Base> funcExclude(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> other = execute(context, focus, exp.getParameters().get(0), true);

    for (Base item : focus) {
      if (!doContains(other, item)) {
        result.add(item);
      }
    }
    return result;
  }


  private List<Base> funcSingle(ExecutionContext context, List<Base> focus, ExpressionNode expr) throws PathEngineException {
    if (focus.size() == 1) {
      return focus;
    }
    throw makeException(expr, I18nConstants.FHIRPATH_NO_COLLECTION, "single", focus.size());
  }


  private List<Base> funcIs(ExecutionContext context, List<Base> focus, ExpressionNode expr) throws PathEngineException {
    if (focus.size() == 0 || focus.size() > 1) {
      return makeNull();
    }
    String ns = null;
    String n = null;

    ExpressionNode texp = expr.getParameters().get(0);
    if (texp.getKind() != Kind.Name) {
      throw makeException(expr, I18nConstants.FHIRPATH_PARAM_WRONG, texp.getKind(), "0", "is");
    }
    if (texp.getInner() != null) {
      if (texp.getInner().getKind() != Kind.Name) {
        throw makeException(expr, I18nConstants.FHIRPATH_PARAM_WRONG, texp.getKind(), "1", "is");
      }
      ns = texp.getName();
      n = texp.getInner().getName();
    } else if (Utilities.existsInList(texp.getName(), "Boolean", "Integer", "Decimal", "String", "DateTime", "Date", "Time", "SimpleTypeInfo", "ClassInfo")) {
      ns = "System";
      n = texp.getName();
    } else {
      ns = "FHIR";
      n = texp.getName();        
    }
    if (ns.equals("System")) {
      if (focus.get(0) instanceof Resource) {
        return makeBoolean(false);
      }
      if (!(focus.get(0) instanceof Element) || ((Element) focus.get(0)).isDisallowExtensions()) {
        String t = Utilities.capitalize(focus.get(0).fhirType());
        if (n.equals(t)) {
          return makeBoolean(true);
        }
        if ("Date".equals(t) && n.equals("DateTime")) {
          return makeBoolean(true);
        } else { 
          return makeBoolean(false);
        }
      } else {
        return makeBoolean(false);
      }
    } else if (ns.equals("FHIR")) {
      if (n.equals(focus.get(0).fhirType())) {
        return makeBoolean(true);
      } else {
        StructureDefinition sd = worker.fetchTypeDefinition(focus.get(0).fhirType());
        while (sd != null) {
          if (n.equals(sd.getType())) {
            return makeBoolean(true);
          }
          sd = worker.fetchResource(StructureDefinition.class, sd.getBaseDefinition(), sd);
        }
        return makeBoolean(false);
      }
    } else { 
      return makeBoolean(false);
    }
  }


  private List<Base> funcAs(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    List<Base> result = new ArrayList<Base>();
    String tn;
    if (expr.getParameters().get(0).getInner() != null) {
      tn = expr.getParameters().get(0).getName()+"."+expr.getParameters().get(0).getInner().getName();
    } else {
      tn = "FHIR."+expr.getParameters().get(0).getName();
    }
    if (!isKnownType(tn)) {
      throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_INVALID_TYPE, tn), I18nConstants.FHIRPATH_INVALID_TYPE);
    }
    if (!doNotEnforceAsSingletonRule && focus.size() > 1) {
      throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_AS_COLLECTION, focus.size(), expr.toString()), I18nConstants.FHIRPATH_AS_COLLECTION); 
    }
    
    for (Base b : focus) {
      if (tn.startsWith("System.")) {
        if (b instanceof Element &&((Element) b).isDisallowExtensions()) { 
          if (b.hasType(tn.substring(7))) {
            result.add(b);
          }
        }

      } else if (tn.startsWith("FHIR.")) {
        String tnp = tn.substring(5);
        if (b.fhirType().equals(tnp)) {
          result.add(b);          
        } else {
          StructureDefinition sd = worker.fetchTypeDefinition(b.fhirType());
          while (sd != null) {
            if (compareTypeNames(tnp, sd.getType())) {
              result.add(b);
              break;
            }
            sd = sd.getKind() == StructureDefinitionKind.PRIMITIVETYPE ? null : worker.fetchResource(StructureDefinition.class, sd.getBaseDefinition(), sd);
          }
        }
      }
    }
    return result;
  }
  

  private List<Base> funcOfType(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    List<Base> result = new ArrayList<Base>();
    String tn;
    if (expr.getParameters().get(0).getInner() != null) {
      tn = expr.getParameters().get(0).getName()+"."+expr.getParameters().get(0).getInner().getName();
    } else {
      tn = "FHIR."+expr.getParameters().get(0).getName();
    }
    if (!isKnownType(tn)) {
      throw new PathEngineException(worker.formatMessage(I18nConstants.FHIRPATH_INVALID_TYPE, tn), I18nConstants.FHIRPATH_INVALID_TYPE); 
    }

    
    for (Base b : focus) {
      if (tn.startsWith("System.")) {
        if (b instanceof Element &&((Element) b).isDisallowExtensions()) { 
          if (b.hasType(tn.substring(7))) {
            result.add(b);
          }
        }

      } else if (tn.startsWith("FHIR.")) {
        String tnp = tn.substring(5);
        if (b.fhirType().equals(tnp)) {
          result.add(b);          
        } else {
          StructureDefinition sd = worker.fetchTypeDefinition(b.fhirType());
          while (sd != null) {
            if (tnp.equals(sd.getType())) {
              result.add(b);
              break;
            }
            sd = sd.getKind() == StructureDefinitionKind.PRIMITIVETYPE ? null : worker.fetchResource(StructureDefinition.class, sd.getBaseDefinition(), sd);
          }
        }
      } else if (tn.startsWith("CDA.")) {
        String tnp = Utilities.pathURL(Constants.NS_CDA_ROOT, "StructureDefinition", tn.substring(4));
        if (b.fhirType().equals(tnp)) {
          result.add(b);          
        } else {
          StructureDefinition sd = worker.fetchTypeDefinition(b.fhirType());
          while (sd != null) {
            if (tnp.equals(sd.getType())) {
              result.add(b);
              break;
            }
            sd = sd.getKind() == StructureDefinitionKind.PRIMITIVETYPE ? null : worker.fetchResource(StructureDefinition.class, sd.getBaseDefinition(), sd);
          }
        }
      }
    }
    return result;
  }

  private List<Base> funcType(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    for (Base item : focus) {
      result.add(new ClassTypeInfo(item));
    }
    return result;
  }


  private List<Base> funcRepeat(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> current = new ArrayList<Base>();
    current.addAll(focus);
    List<Base> added = new ArrayList<Base>();
    boolean more = true;
    while (more) {
      added.clear();
      List<Base> pc = new ArrayList<Base>();
      for (Base item : current) {
        pc.clear();
        pc.add(item);
        added.addAll(execute(changeThis(context, item), pc, exp.getParameters().get(0), false));
      }
      more = false;
      current.clear();
      for (Base b : added) {
        boolean isnew = true;
        for (Base t : result) {
          if (b.equalsDeep(t)) {
            isnew = false;
          }
        }
        if (isnew) {
          result.add(b);
          current.add(b);
          more = true;
        }
      }
    }
    return result;
  }


  private List<Base> funcAggregate(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> total = new ArrayList<Base>();
    if (exp.parameterCount() > 1) {
      total = execute(context, focus, exp.getParameters().get(1), false);
    }

    List<Base> pc = new ArrayList<Base>();
    for (Base item : focus) {
      ExecutionContext c = changeThis(context, item);
      c.total = total;
      c.next();
      total = execute(c, pc, exp.getParameters().get(0), true);
    }
    return total;
  }



  private List<Base> funcIsDistinct(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    if (focus.size() < 1) {
      return makeBoolean(true);
    }
    if (focus.size() == 1) {
      return makeBoolean(true);
    }

    boolean distinct = true;
    for (int i = 0; i < focus.size(); i++) {
      for (int j = i+1; j < focus.size(); j++) {
        Boolean eq = doEquals(focus.get(j), focus.get(i));
        if (eq == null) {
          return new ArrayList<Base>();
        } else if (eq == true) {
          distinct = false;
          break;
        }
      }
    }
    return makeBoolean(distinct);
  }


  private List<Base> funcSupersetOf(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> target = execute(context, focus, exp.getParameters().get(0), true);

    boolean valid = true;
    for (Base item : target) {
      boolean found = false;
      for (Base t : focus) {
        if (Base.compareDeep(item, t, false)) {
          found = true;
          break;
        }
      }
      if (!found) {
        valid = false;
        break;
      }
    }
    List<Base> result = new ArrayList<Base>();
    result.add(new BooleanType(valid).noExtensions());
    return result;
  }


  private List<Base> funcSubsetOf(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> target = execute(context, focus, exp.getParameters().get(0), true);

    boolean valid = true;
    for (Base item : focus) {
      boolean found = false;
      for (Base t : target) {
        if (Base.compareDeep(item, t, false)) {
          found = true;
          break;
        }
      }
      if (!found) {
        valid = false;
        break;
      }
    }
    List<Base> result = new ArrayList<Base>();
    result.add(new BooleanType(valid).noExtensions());
    return result;
  }


  private List<Base> funcExists(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    boolean empty = true;
    List<Base> pc = new ArrayList<Base>();
    for (Base f : focus) {
      if (exp.getParameters().size() == 1) {
        pc.clear();
        pc.add(f);
        Equality v = asBool(execute(changeThis(context, f), pc, exp.getParameters().get(0), true), exp);
        if (v == Equality.True) {
          empty = false;
        }
      } else if (!f.isEmpty()) {
        empty = false;
      }
    }
    result.add(new BooleanType(!empty).noExtensions());
    return result;
  }


  private List<Base> funcResolve(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    Base refContext = null;
    for (Base item : focus) {
      String s = convertToString(item);
      if (item.fhirType().equals("Reference")) {
        refContext = item;
        Property p = item.getChildByName("reference");
        if (p != null && p.hasValues()) {
          s = convertToString(p.getValues().get(0));
        } else {
          s = null; // a reference without any valid actual reference (just identifier or display, but we can't resolve it)
        }
      }
      if (item.fhirType().equals("canonical")) {
        s = item.primitiveValue();
        refContext = item;
      }
      if (s != null) {
        Base res = null;
        if (s.startsWith("#")) {
          String t = s.substring(1);
          Property p = context.rootResource.getChildByName("contained");
          if (p != null) {
            for (Base c : p.getValues()) {
              if (t.equals(c.getIdBase())) {
                res = c;
                break;
              }
            }
          }
        } else if (hostServices != null) {
          try {
            res = hostServices.resolveReference(this, context.appInfo, s, refContext);
          } catch (Exception e) {
            res = null;
          }
        }
        if (res != null) {
          result.add(res);
        }
      }
    }

    return result;
  }

  private List<Base> funcExtension(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String url = nl.get(0).primitiveValue();

    for (Base item : focus) {
      List<Base> ext = new ArrayList<Base>();
      getChildrenByName(item, "extension", ext);
      getChildrenByName(item, "modifierExtension", ext);
      for (Base ex : ext) {
        List<Base> vl = new ArrayList<Base>();
        getChildrenByName(ex, "url", vl);
        if (convertToString(vl).equals(url)) {
          result.add(ex);
        }
      }
    }
    return result;
  }

  private List<Base> funcAllFalse(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (exp.getParameters().size() == 1) {
      boolean all = true;
      List<Base> pc = new ArrayList<Base>();
      for (Base item : focus) {
        pc.clear();
        pc.add(item);
        List<Base> res = execute(context, pc, exp.getParameters().get(0), true);
        Equality v = asBool(res, exp);
        if (v != Equality.False) {
          all = false;
          break;
        }
      }
      result.add(new BooleanType(all).noExtensions());
    } else { 
      boolean all = true;
      for (Base item : focus) {
        if (!canConvertToBoolean(item)) {
          throw new FHIRException("Unable to convert '"+convertToString(item)+"' to a boolean");
        }

        Equality v = asBool(item, true);
        if (v != Equality.False) {
          all = false;
          break;
        }
      }
      result.add(new BooleanType(all).noExtensions());
    }
    return result;
  }

  private List<Base> funcAnyFalse(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (exp.getParameters().size() == 1) {
      boolean any = false;
      List<Base> pc = new ArrayList<Base>();
      for (Base item : focus) {
        pc.clear();
        pc.add(item);
        List<Base> res = execute(context, pc, exp.getParameters().get(0), true);
        Equality v = asBool(res, exp);
        if (v == Equality.False) {
          any = true;
          break;
        }
      }
      result.add(new BooleanType(any).noExtensions());
    } else {
      boolean any = false;
      for (Base item : focus) {
        if (!canConvertToBoolean(item)) {
          throw new FHIRException("Unable to convert '"+convertToString(item)+"' to a boolean");
        }

        Equality v = asBool(item, true);
        if (v == Equality.False) {
          any = true;
          break;
        }
      }
      result.add(new BooleanType(any).noExtensions());
    }
    return result;
  }

  private List<Base> funcAllTrue(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (exp.getParameters().size() == 1) {
      boolean all = true;
      List<Base> pc = new ArrayList<Base>();
      for (Base item : focus) {
        pc.clear();
        pc.add(item);
        List<Base> res = execute(context, pc, exp.getParameters().get(0), true);
        Equality v = asBool(res, exp);
        if (v != Equality.True) {
          all = false;
          break;
        }
      }
      result.add(new BooleanType(all).noExtensions());
    } else { 
      boolean all = true;
      for (Base item : focus) {
        if (!canConvertToBoolean(item)) {
          throw new FHIRException("Unable to convert '"+convertToString(item)+"' to a boolean");
        }
        Equality v = asBool(item, true);
        if (v != Equality.True) {
          all = false;
          break;
        }
      }
      result.add(new BooleanType(all).noExtensions());
    }
    return result;
  }

  private List<Base> funcAnyTrue(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (exp.getParameters().size() == 1) {
      boolean any = false;
      List<Base> pc = new ArrayList<Base>();
      for (Base item : focus) {
        pc.clear();
        pc.add(item);
        List<Base> res = execute(context, pc, exp.getParameters().get(0), true);
        Equality v = asBool(res, exp);
        if (v == Equality.True) {
          any = true;
          break;
        }
      }
      result.add(new BooleanType(any).noExtensions());
    } else {
      boolean any = false;
      for (Base item : focus) {
        if (!canConvertToBoolean(item)) {
          throw new FHIRException("Unable to convert '"+convertToString(item)+"' to a boolean");
        }

        Equality v = asBool(item, true);
        if (v == Equality.True) {
          any = true;
          break;
        }
      }
      result.add(new BooleanType(any).noExtensions());
    }
    return result;
  }

  private boolean canConvertToBoolean(Base item) {
    return (item.isBooleanPrimitive());
  }

  private List<Base> funcTrace(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String name = nl.get(0).primitiveValue();
    if (exp.getParameters().size() == 2) {
      List<Base> n2 = execute(context, focus, exp.getParameters().get(1), true);
      log(name, n2);
    } else { 
      log(name, focus);
    }
    return focus;
  }

  private List<Base> funcDefineVariable(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> nl = execute(context, focus, exp.getParameters().get(0), true);
    String name = nl.get(0).primitiveValue();
    List<Base> value;
    if (exp.getParameters().size() == 2) {
      value = execute(context, focus, exp.getParameters().get(1), true);
    } else { 
      value = focus;
    }
    // stash the variable into the context
    context.setDefinedVariable(name, value);
    return focus;
  }

  private List<Base> funcCheck(ExecutionContext context, List<Base> focus, ExpressionNode expr) throws FHIRException {
    List<Base> n1 = execute(context, focus, expr.getParameters().get(0), true);
    if (!convertToBoolean(n1)) {
      List<Base> n2 = execute(context, focus, expr.getParameters().get(1), true);
      String name = n2.get(0).primitiveValue();
      throw makeException(expr, I18nConstants.FHIRPATH_CHECK_FAILED, name);
    }
    return focus;
  }

  private List<Base> funcDistinct(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    if (focus.size() <= 1) {
      return focus;
    }

    List<Base> result = new ArrayList<Base>();
    for (int i = 0; i < focus.size(); i++) {
      boolean found = false;
      for (int j = i+1; j < focus.size(); j++) {
        Boolean eq = doEquals(focus.get(j), focus.get(i));
        if (eq == null)
          return new ArrayList<Base>();
        else if (eq == true) {
          found = true;
          break;
        }
      }
      if (!found) {
        result.add(focus.get(i));
      }
    }
    return result;
  }

  private List<Base> funcMatches(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> swb = execute(context, focus, exp.getParameters().get(0), true);
    String sw = convertToString(swb);

    if (focus.size() == 0 || swb.size() == 0) {
      //
    } else if (focus.size() == 1 && !Utilities.noString(sw)) {
      if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
        String st = convertToString(focus.get(0));
        if (Utilities.noString(st)) {
          result.add(new BooleanType(false).noExtensions());
        } else {
          Pattern p = Pattern.compile("(?s)" + sw);
          Matcher m = p.matcher(st);
          boolean ok = m.find();
          result.add(new BooleanType(ok).noExtensions());
        }
      }
    } else {
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcMatchesFull(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    String sw = convertToString(execute(context, focus, exp.getParameters().get(0), true));

    if (focus.size() == 1 && !Utilities.noString(sw)) {
      if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
        String st = convertToString(focus.get(0));
        if (Utilities.noString(st)) {
          result.add(new BooleanType(false).noExtensions());
        } else {
          Pattern p = Pattern.compile("(?s)" + sw);
          Matcher m = p.matcher(st);
          boolean ok = m.matches();
          result.add(new BooleanType(ok).noExtensions());
        }
      }
    } else {
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcContains(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> swb = execute(context, focus, exp.getParameters().get(0), true);
    String sw = convertToString(swb);

    if (focus.size() != 1) {
      //
    } else if (swb.size() != 1) {
        //
    } else if (Utilities.noString(sw)) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
      String st = convertToString(focus.get(0));
      if (Utilities.noString(st)) {
        result.add(new BooleanType(false).noExtensions());
      } else {
        result.add(new BooleanType(st.contains(sw)).noExtensions());
      }
    } 
    return result;
  }

  private List<Base> baseToList(Base b) {
    List<Base> res = new ArrayList<>();
    res.add(b);
    return res;
  }

  private List<Base> funcLength(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1 && (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion)) {
      String s = convertToString(focus.get(0));
      result.add(new IntegerType(s.length()).noExtensions());
    }
    return result;
  }

  private List<Base> funcHasValue(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1) {
      String s = convertToString(focus.get(0));
      result.add(new BooleanType(!Utilities.noString(s)).noExtensions());
    } else {
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcStartsWith(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> swb = execute(context, focus, exp.getParameters().get(0), true);
    String sw = convertToString(swb);

    if (focus.size() == 0) {
      // no result
    } else if (swb.size() == 0) {
      // no result
    } else if (Utilities.noString(sw)) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
      String s = convertToString(focus.get(0));
      if (s == null) {
        result.add(new BooleanType(false).noExtensions());
      } else {
        result.add(new BooleanType(s.startsWith(sw)).noExtensions());
      }
    }
    return result;
  }

  private List<Base> funcLower(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1 && (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion)) {
      String s = convertToString(focus.get(0));
      if (!Utilities.noString(s)) { 
        result.add(new StringType(s.toLowerCase()).noExtensions());
      }
    }
    return result;
  }

  private List<Base> funcUpper(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1 && (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion)) {
      String s = convertToString(focus.get(0));
      if (!Utilities.noString(s)) { 
        result.add(new StringType(s.toUpperCase()).noExtensions());
      }
    }
    return result;
  }

  private List<Base> funcToChars(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 1 && (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion)) {
      String s = convertToString(focus.get(0));
      for (char c : s.toCharArray()) {  
        result.add(new StringType(String.valueOf(c)).noExtensions());
      }
    }
    return result;
  }

  private List<Base> funcIndexOf(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 0) { 
      // no result, and don't need to do anything (including evaluate the parameter)
      return result;
    }

    List<Base> swb = execute(context, focus, exp.getParameters().get(0), true);
    String sw = convertToString(swb);
    if (swb.size() == 0) {
      // no result
    } else if (Utilities.noString(sw)) {
      result.add(new IntegerType(0).noExtensions());
    } else if (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion) {
      String s = convertToString(focus.get(0));
      if (s == null) {
        result.add(new IntegerType(0).noExtensions());
      } else {
        result.add(new IntegerType(s.indexOf(sw)).noExtensions());
      }
    }
    return result;
  }

  private List<Base> funcSubstring(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 0) {
      // if there is no focus, then we don't need to do anything (including evaluate the parameter(s))
      return result;
    }

    List<Base> n1 = execute(context, focus, exp.getParameters().get(0), true);
    if (n1.size() == 0) {
      // the start parameter is not present, so return an empty list)
      return result;
    }
    int i1 = Integer.parseInt(n1.get(0).primitiveValue());
    int i2 = -1;
    if (exp.parameterCount() == 2) {
      List<Base> n2 = execute(context, focus, exp.getParameters().get(1), true);
      if (n2.isEmpty()|| !n2.get(0).isPrimitive() || !Utilities.isInteger(n2.get(0).primitiveValue())) {
        return new ArrayList<Base>();
      }
      i2 = Integer.parseInt(n2.get(0).primitiveValue());
    }

    if (focus.size() == 1 && (focus.get(0).hasType(FHIR_TYPES_STRING) || doImplicitStringConversion)) {
      String sw = convertToString(focus.get(0));
      String s;
      if (i1 < 0 || i1 >= sw.length()) {
        return new ArrayList<Base>();
      }
      if (exp.parameterCount() == 2) {
        s = sw.substring(i1, Math.min(sw.length(), i1+i2));
      } else {
        s = sw.substring(i1);
      }
      if (!Utilities.noString(s)) { 
        result.add(new StringType(s).noExtensions());
      }
    }
    return result;
  }

  private List<Base> funcToInteger(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    String s = convertToString(focus);
    List<Base> result = new ArrayList<Base>();
    if (Utilities.isInteger(s)) {
      result.add(new IntegerType(s).noExtensions());
    } else if ("true".equals(s)) {
      result.add(new IntegerType(1).noExtensions());
    } else if ("false".equals(s)) {
      result.add(new IntegerType(0).noExtensions());
    }
    return result;
  }

  private List<Base> funcIsInteger(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (focus.get(0) instanceof IntegerType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof BooleanType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof StringType) {
      result.add(new BooleanType(Utilities.isInteger(convertToString(focus.get(0)))).noExtensions());
    } else { 
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcIsBoolean(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (focus.get(0) instanceof IntegerType) {
      result.add(new BooleanType(((IntegerType) focus.get(0)).getValue() >= 0 && ((IntegerType) focus.get(0)).getValue() <= 1).noExtensions());
    } else if (focus.get(0) instanceof DecimalType) {
      result.add(new BooleanType(((DecimalType) focus.get(0)).getValue().compareTo(BigDecimal.ZERO) == 0 || ((DecimalType) focus.get(0)).getValue().compareTo(BigDecimal.ONE) == 0).noExtensions());
    } else if (focus.get(0) instanceof BooleanType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof StringType) {
      result.add(new BooleanType(Utilities.existsInList(convertToString(focus.get(0)).toLowerCase(), "true", "false")).noExtensions());
    } else { 
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcIsDateTime(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (focus.get(0) instanceof DateTimeType || focus.get(0) instanceof DateType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof StringType) {
      result.add(new BooleanType((convertToString(focus.get(0)).matches
          ("([0-9]([0-9]([0-9][1-9]|[1-9]0)|[1-9]00)|[1-9]000)(-(0[1-9]|1[0-2])(-(0[1-9]|[1-2][0-9]|3[0-1])(T([01][0-9]|2[0-3])(:[0-5][0-9](:([0-5][0-9]|60))?)?(\\.[0-9]+)?(Z|(\\+|-)((0[0-9]|1[0-3]):[0-5][0-9]|14:00))?)?)?)?"))).noExtensions());
    } else { 
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcIsDate(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (focus.get(0) instanceof DateTimeType || focus.get(0) instanceof DateType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof StringType) {
      result.add(new BooleanType((convertToString(focus.get(0)).matches
          ("([0-9]([0-9]([0-9][1-9]|[1-9]0)|[1-9]00)|[1-9]000)(-(0[1-9]|1[0-2])(-(0[1-9]|[1-2][0-9]|3[0-1])(T([01][0-9]|2[0-3])(:[0-5][0-9](:([0-5][0-9]|60))?)?(\\.[0-9]+)?(Z|(\\+|-)((0[0-9]|1[0-3]):[0-5][0-9]|14:00))?)?)?)?"))).noExtensions());
    } else { 
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcConformsTo(ExecutionContext context, List<Base> focus, ExpressionNode expr) throws FHIRException {
    if (hostServices == null) {
      throw makeException(expr, I18nConstants.FHIRPATH_HO_HOST_SERVICES, "conformsTo");
    }
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else {
      String url = convertToString(execute(context, focus, expr.getParameters().get(0), true));
      result.add(new BooleanType(hostServices.conformsToProfile(this, context.appInfo,  focus.get(0), url)).noExtensions());
    }
    return result;
  }

  private List<Base> funcIsTime(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (focus.get(0) instanceof TimeType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof StringType) {
      result.add(new BooleanType((convertToString(focus.get(0)).matches
          ("(T)?([01][0-9]|2[0-3])(:[0-5][0-9](:([0-5][0-9]|60))?)?(\\.[0-9]+)?(Z|(\\+|-)((0[0-9]|1[0-3]):[0-5][0-9]|14:00))?"))).noExtensions());
    } else {
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcIsString(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (!(focus.get(0) instanceof DateTimeType) && !(focus.get(0) instanceof TimeType)) {
      result.add(new BooleanType(true).noExtensions());
    } else { 
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  private List<Base> funcIsQuantity(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (focus.get(0) instanceof IntegerType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof DecimalType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (makeQuantity(focus.get(0)) instanceof Quantity) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof BooleanType) {
      result.add(new BooleanType(true).noExtensions());
    } else  if (focus.get(0) instanceof StringType) {
      Quantity q = parseQuantityString(focus.get(0).primitiveValue());
      result.add(new BooleanType(q != null).noExtensions());
    } else {
      result.add(new BooleanType(false).noExtensions());
    }
    return result;
  }

  public Quantity parseQuantityString(String s) {
    if (s == null) {
      return null;
    }
    s = s.trim();
    if (s.contains(" ")) {
      String v = s.substring(0, s.indexOf(" ")).trim();
      s = s.substring(s.indexOf(" ")).trim();
      if (!Utilities.isDecimal(v, false)) {
        return null;
      }
      if (s.startsWith("'") && s.endsWith("'")) {
        return Quantity.fromUcum(v, s.substring(1, s.length()-1));
      }
      if (s.equals("year") || s.equals("years")) {
        return Quantity.fromUcum(v, "a");
      } else if (s.equals("month") || s.equals("months")) {
        return Quantity.fromUcum(v, "mo_s");
      } else if (s.equals("week") || s.equals("weeks")) {
        return Quantity.fromUcum(v, "wk");
      } else if (s.equals("day") || s.equals("days")) {
        return Quantity.fromUcum(v, "d");
      } else if (s.equals("hour") || s.equals("hours")) {
        return Quantity.fromUcum(v, "h");
      } else if (s.equals("minute") || s.equals("minutes")) {
        return Quantity.fromUcum(v, "min");
      } else if (s.equals("second") || s.equals("seconds")) {
        return Quantity.fromUcum(v, "s");
      } else if (s.equals("millisecond") || s.equals("milliseconds")) {
        return Quantity.fromUcum(v, "ms");
      } else {
        return null;
      } 
    } else {
      if (Utilities.isDecimal(s, true)) {
        return new Quantity().setValue(new BigDecimal(s)).setSystem("http://unitsofmeasure.org").setCode("1");
      } else {
        return null;
      } 
    }
  }


  private List<Base> funcIsDecimal(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() != 1) {
      result.add(new BooleanType(false).noExtensions());
    } else if (focus.get(0) instanceof IntegerType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof BooleanType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof DecimalType) {
      result.add(new BooleanType(true).noExtensions());
    } else if (focus.get(0) instanceof StringType) {
      result.add(new BooleanType(Utilities.isDecimal(convertToString(focus.get(0)), true)).noExtensions());
    } else {
      result.add(new BooleanType(false).noExtensions());
    } 
    return result;
  }

  private List<Base> funcCount(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    result.add(new IntegerType(focus.size()).noExtensions());
    return result;
  }

  private List<Base> funcSkip(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> n1 = execute(context, focus, exp.getParameters().get(0), true);
    int i1 = Integer.parseInt(n1.get(0).primitiveValue());

    List<Base> result = new ArrayList<Base>();
    for (int i = i1; i < focus.size(); i++) {
      result.add(focus.get(i));
    } 
    return result;
  }

  private List<Base> funcTail(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    for (int i = 1; i < focus.size(); i++) {
      result.add(focus.get(i));
    } 
    return result;
  }


  private class FHIRPathBaseSorter implements Comparator<Base> {

    private ExecutionContext context;
    private ExpressionNode expr;

    public FHIRPathBaseSorter(IWorkerContext worker, ExecutionContext context, ExpressionNode expr) {
      this.context = context;
      this.expr = expr;
    }

    @Override
    public int compare(Base o1, Base o2) {
      if (expr.getParameters().size() == 0) {
        // natural sort order
        return compareNatural(o1, o2, null);
      }
      for (ExpressionNode p : expr.getParameters()) {
        boolean reversed = false;
        ExpressionNode pf = p;
        if (pf.getKind() == Kind.Unary) {
          reversed = true;
          pf = pf.getOpNext();
        }
        Base b1 = executeExpression(o1, pf);  
        Base b2 = executeExpression(o2, pf);
        int res = compareNatural(b1, b2, pf.toString());
        if (res != 0) {
          return reversed ? -res : res;
        }
      }    
      return 0;
    }

    private Base executeExpression(Base b, ExpressionNode pf) {
      List<Base> focus = new ArrayList<Base>();
      focus.add(b);
      focus = execute(changeThis(context, b), focus, pf, true);
      if (focus.size() == 0) {
        return null;
      } else if (focus.size() > 1) {
        throw new FHIRException(worker.formatMessage(I18nConstants.FHIRPATH_MUTIPLE_VALUES_IN_SORT, pf.toString()));
      } else {
        return focus.get(0);
      }
    }

    private int compareNatural(Base o1, Base o2, String sorter) {
      if (o1 == null && o2 == null) {
        return 0;
      }
      if (o1 == null) {
        return 1;
      }
      if (o2 == null) {
        return -1;
      }
      
      if (!isComparableTypes(o1.fhirType(), o2.fhirType())) {
        throw new FHIRException(worker.formatMessage(sorter == null ? I18nConstants.FHIRPATH_MUTIPLE_SORT_TYPE_PROBLEM_NATURAL : I18nConstants.FHIRPATH_MUTIPLE_SORT_TYPE_PROBLEM, o1.fhirType(), o2.fhirType(), sorter));
      }
      String s1 = o1.primitiveValue();
      String s2 = o2.primitiveValue();
      if (Utilities.existsInList(o1.fhirType(), "integer", "unsignedInt", "positiveInt", "integer64")) {
        return Integer.compare(Integer.parseInt(s1),Integer.parseInt(s2));
      } else if (Utilities.existsInList(o1.fhirType(), "decimal")) {
        return Double.compare(Double.parseDouble(s1),Double.parseDouble(s2));
      } else if (Utilities.existsInList(o1.fhirType(), "boolean")) {
        return s2.compareTo(s1); // order is deliberately reverse
      } else {
        return s1.compareTo(s2); // order is deliberately reverse
      }
    }

    private boolean isComparableTypes(String t1, String t2) {
      if (!Utilities.existsInList(t1, "integer", "unsignedInt", "positiveInt", "decimal", "boolean", "date", "dateTime", "time", "instant", "string", "code", "url", "uri", "uuid", "oid", "canonical", "integer64")) {
        return false;
      }
      if (!Utilities.existsInList(t2, "integer", "unsignedInt", "positiveInt", "decimal", "boolean", "date", "dateTime", "time", "instant", "string", "code", "url", "uri", "uuid", "oid", "canonical", "integer64")) {
        return false;
      }
      if (Utilities.existsInList(t1, "integer", "unsignedInt", "positiveInt", "integer64") && Utilities.existsInList(t2, "integer", "unsignedInt", "positiveInt", "integer64")) {
        return true;
      }
      if (Utilities.existsInList(t1, "boolean") && Utilities.existsInList(t2, "boolean")) {
        return true;
      }
      if (Utilities.existsInList(t1, "decimal") && Utilities.existsInList(t2, "decimal")) {
        return true;
      }
      if (Utilities.existsInList(t1, "time") && Utilities.existsInList(t2, "time")) {
        return true;
      }
      if (Utilities.existsInList(t1, "date", "dateTime", "instant") && Utilities.existsInList(t2, "date", "dateTime", "instant")) {
        return true;
      }
      if (Utilities.existsInList(t1, "string", "code", "url", "uri", "uuid", "oid", "canonical") && Utilities.existsInList(t2, "string", "code", "url", "uri", "uuid", "oid", "canonical")) {
        return true;
      }
      return false;
    }

  }

  private List<Base> funcSort(ExecutionContext context, List<Base> focus, ExpressionNode expr) {
    List<Base> result = new ArrayList<Base>();
    result.addAll(focus);
    Collections.sort(result, new FHIRPathBaseSorter(this.getWorker(), context, expr));
    return result;  
  }

  
  private List<Base> funcLast(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() > 0) {
      result.add(focus.get(focus.size()-1));
    } 
    return result;
  }

  private List<Base> funcFirst(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() > 0) {
      result.add(focus.get(0));
    } 
    return result;
  }


  private List<Base> funcWhere(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> pc = new ArrayList<Base>();
    for (Base item : focus) {
      pc.clear();
      pc.add(item);
      Equality v = asBool(execute(changeThis(context, item), pc, exp.getParameters().get(0), true), exp);
      if (v == Equality.True) {
        result.add(item);
      } 
    }
    return result;
  }

  private List<Base> funcSelect(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> pc = new ArrayList<Base>();
    int i = 0;
    for (Base item : focus) {
      pc.clear();
      pc.add(item);
      result.addAll(execute(changeThis(context, item).setIndex(i), pc, exp.getParameters().get(0), true));
      i++;
    }
    return result;
  }

  private List<Base> funcCoalesce(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    // iterate over all the parameters, and return the first one that has a value
    for (ExpressionNode p : exp.getParameters()) {
      List<Base> pc = execute(context, focus, p, true);
      if (pc.size() > 0) {
        return pc;
      }
    }

    // no result from any of the parameters, so return an empty list
    List<Base> result = new ArrayList<Base>();
    return result;
  }

  private List<Base> funcItem(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    String s = convertToString(execute(context, focus, exp.getParameters().get(0), true));
    if (Utilities.isInteger(s) && Integer.parseInt(s) < focus.size()) {
      result.add(focus.get(Integer.parseInt(s)));
    } 
    return result;
  }

  private List<Base> funcEmpty(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    result.add(new BooleanType(ElementUtil.isEmpty(focus)).noExtensions());
    return result;
  }

  private List<Base> funcNot(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws PathEngineException {
    List<Base> result = new ArrayList<Base>();  
    Equality v = asBool(focus, exp);
    if (v != Equality.Null) {
      result.add(new BooleanType(v != Equality.True));
    } 
    return result;
  }

  private class ElementDefinitionMatch {
    private ElementDefinition definition;
    private ElementDefinition sourceDefinition; // if there was a content reference
    private String fixedType;
    public ElementDefinitionMatch(ElementDefinition definition, String fixedType) {
      super();
      this.definition = definition;
      this.fixedType = fixedType;
    }
    public ElementDefinition getDefinition() {
      return definition;
    }
    public ElementDefinition getSourceDefinition() {
      return sourceDefinition;
    }
    public String getFixedType() {
      return fixedType;
    }

  }

  private void getChildTypesByName(String type, String name, TypeDetails result, ExpressionNode expr, TypeDetails focus, Set<ElementDefinition> elementDependencies) throws PathEngineException, DefinitionException {
    if (Utilities.noString(type)) {
      throw makeException(expr, I18nConstants.FHIRPATH_NO_TYPE, "", "getChildTypesByName");
    } 
    if (type.equals("http://hl7.org/fhir/StructureDefinition/xhtml")) {
      return;
    }     

    if (type.equals(TypeDetails.FP_SimpleTypeInfo)) { 
      getSimpleTypeChildTypesByName(name, result);
    } else if (type.equals(TypeDetails.FP_ClassInfo)) { 
      getClassInfoChildTypesByName(name, result);
    } else {
      if (type.startsWith(Constants.NS_SYSTEM_TYPE)) {
        return;
      } 
      
      String url = null;
      if (type.contains("#")) {
        url = type.substring(0, type.indexOf("#"));
      } else {
        url = type;
      }
      String tail = "";
      StructureDefinition sd = worker.fetchTypeDefinition(url);
      if (sd == null) {
        sd = worker.fetchResource(StructureDefinition.class, url);
      }
      if (sd == null) {
        if (url.startsWith(TypeDetails.FP_NS)) {
          return;
        } else {
          throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_TYPE, url, "getChildTypesByName#1");          
        }
      }
      List<StructureDefinition> sdl = new ArrayList<StructureDefinition>();
      ElementDefinitionMatch m = null;
      if (type.contains("#")) {
        List<ElementDefinitionMatch> list = getElementDefinition(sd, type.substring(type.indexOf("#")+1), false, expr);
        m = list.size() == 1 ? list.get(0) : null;
      }
      if (m != null && hasDataType(m.definition)) {
        if (m.fixedType != null)  {
          StructureDefinition dt = worker.fetchResource(StructureDefinition.class, ProfileUtilities.sdNs(m.fixedType, null), sd);
          if (dt == null) {
            throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_TYPE, ProfileUtilities.sdNs(m.fixedType, null), "getChildTypesByName#2");
          }
          sdl.add(dt);
        } else
          for (TypeRefComponent t : m.definition.getType()) {
            StructureDefinition dt = worker.fetchResource(StructureDefinition.class, ProfileUtilities.sdNs(t.getCode(), null));
            if (dt == null) {
              throw makeException(expr, I18nConstants.FHIRPATH_UNKNOWN_TYPE, ProfileUtilities.sdNs(t.getCode(), null), "getChildTypesByName#3");
            }
            addTypeAndDescendents(sdl, dt, cu.allStructures());
            // also add any descendant types
          }
      } else {
        addTypeAndDescendents(sdl, sd, cu.allStructures());
        if (type.contains("#")) {
          tail = type.substring(type.indexOf("#")+1);
          if (tail.contains(".")) {
            tail = tail.substring(tail.indexOf("."));
          } else {
            tail = "";
          }
        }
      }

      for (StructureDefinition sdi : sdl) {
        String path = sdi.getSnapshot().getElement().get(0).getPath()+tail+".";
        if (name.equals("**")) {
          assert(result.getCollectionStatus() == CollectionStatus.UNORDERED);
          for (ElementDefinition ed : sdi.getSnapshot().getElement()) {
            if (ed.getPath().startsWith(path)) {
              if (ed.hasContentReference()) {
                String cpath = ed.getContentReference();
                if (!cpath.startsWith("#")) {
                  if (!cpath.contains("#")) {
                    throw new Error("ContentReference doesn't contain a #: "+cpath);
                  }
                  cpath = cpath.substring(cpath.indexOf("#"));
                }
                String tn = sdi.getType()+cpath;
                if (!result.hasType(worker, tn)) {
                  if (elementDependencies != null) {
                    elementDependencies.add(ed);
                  }
                  getChildTypesByName(result.addType(tn), "**", result, expr, null, elementDependencies);
                }
              } else {
                for (TypeRefComponent t : ed.getType()) {
                  if (t.hasCode() && t.getCodeElement().hasValue()) {
                    String tn = null;
                    if (Utilities.existsInList(t.getCode(), "Element", "BackboneElement", "Base") || cu.isAbstractType(t.getCode())) {
                      tn = sdi.getType()+"#"+ed.getPath();
                    } else {
                      tn = t.getCode();
                    }
                    if (t.getCode().equals("Resource")) {
                      for (String rn : worker.getResourceNames()) {
                        if (!result.hasType(worker, rn)) {
                          if (elementDependencies != null) {
                            elementDependencies.add(ed);
                          }
                          getChildTypesByName(result.addType(rn), "**", result, expr, null, elementDependencies);
                        }                  
                      }
                    } else if (!result.hasType(worker, tn)) {
                      if (elementDependencies != null) {
                        elementDependencies.add(ed);
                      }
                      getChildTypesByName(result.addType(tn), "**", result, expr, null, elementDependencies);
                    }
                  }
                }
              }
            }
          }      
        } else if (name.equals("*")) {
          assert(result.getCollectionStatus() == CollectionStatus.UNORDERED);
          for (ElementDefinition ed : sdi.getSnapshot().getElement()) {
            if (ed.getPath().startsWith(path) && !ed.getPath().substring(path.length()).contains("."))
              for (TypeRefComponent t : ed.getType()) {
                if (Utilities.noString(t.getCode())) { // Element.id or Extension.url
                  if (elementDependencies != null) {
                    elementDependencies.add(ed);
                  }
                  result.addType("System.string");
                } else if (t.getCode().equals("Element") || t.getCode().equals("BackboneElement")) {
                  if (elementDependencies != null) {
                    elementDependencies.add(ed);
                  }
                  result.addType(sdi.getType()+"#"+ed.getPath());
                } else if (t.getCode().equals("Resource")) {
                  if (elementDependencies != null) {
                    elementDependencies.add(ed);
                  }
                  result.addTypes(worker.getResourceNames());
                } else {
                  if (elementDependencies != null) {
                    elementDependencies.add(ed);
                  }
                  result.addType(t.getCode());
                  copyTargetProfiles(ed, t, focus, result);
                }
              }
          }
        } else {
          path = sdi.getSnapshot().getElement().get(0).getPath()+tail+"."+name;

          List<ElementDefinitionMatch> edl = getElementDefinition(sdi, path, isAllowPolymorphicNames(), expr);
          for (ElementDefinitionMatch ed : edl) {
            if (ed.getDefinition().isChoice()) {
              result.setChoice(true);
            }
            if (!Utilities.noString(ed.getFixedType())) {
              if (elementDependencies != null) {
                elementDependencies.add(ed.definition);
              }
              result.addType(ed.getFixedType());
            } else if (ed.getSourceDefinition() != null) {
              ProfiledType pt = new ProfiledType(sdi.getType()+"#"+ed.definition.getPath());
              result.addType(ed.getSourceDefinition().unbounded() ? CollectionStatus.ORDERED : CollectionStatus.SINGLETON, pt);
            } else {
              for (TypeRefComponent t : ed.getDefinition().getType()) {
                if (Utilities.noString(t.getCode())) {
                  if (Utilities.existsInList(ed.getDefinition().getId(), "Element.id", "Extension.url") || Utilities.existsInList(ed.getDefinition().getBase().getPath(), "Resource.id", "Element.id", "Extension.url")) { 
                    if (elementDependencies != null) {
                      elementDependencies.add(ed.definition);
                    }
                    result.addType(TypeDetails.FP_NS, "System.String");
                  }
                  break; // throw new PathEngineException("Illegal reference to primitive value attribute @ "+path);
                }

                ProfiledType pt = null;
                if (t.getCode().equals("Element") || t.getCode().equals("BackboneElement") || isAbstractType(t.getCode())) {
                  pt = new ProfiledType(sdi.getUrl()+"#"+path);
                } else if (t.getCode().equals("Resource")) {
                  if (elementDependencies != null) {
                    elementDependencies.add(ed.definition);
                  }
                  result.addTypes(worker.getResourceNames());
                } else {
                  pt = new ProfiledType(t.getWorkingCode());
                }
                if (pt != null) {
                  if (t.hasProfile()) {
                    pt.addProfiles(t.getProfile());
                  }
                  if (ed.getDefinition().hasBinding()) {
                    pt.addBinding(ed.getDefinition().getBinding());
                  }
                  if (elementDependencies != null) {
                    elementDependencies.add(ed.definition);
                  }
                  result.addType(ed.definition.unbounded() ? CollectionStatus.ORDERED : CollectionStatus.SINGLETON, pt);
                  copyTargetProfiles(ed.getDefinition(), t, focus, result);
                }
              }
            }
          }
        }
      }
    }
  }

  private void copyTargetProfiles(ElementDefinition ed, TypeRefComponent t, TypeDetails focus, TypeDetails result) {
    if (t.hasTargetProfile()) {
      for (CanonicalType u : t.getTargetProfile()) {
        result.addTarget(u.primitiveValue());
      }
    } else if (focus != null && focus.hasType("CodeableReference") && ed.getPath().endsWith(".reference") && focus.getTargets() != null) { // special case, targets are on parent
      for (String s : focus.getTargets()) {
        result.addTarget(s);
      }
    }
  }

  private void addTypeAndDescendents(List<StructureDefinition> sdl, StructureDefinition dt, List<StructureDefinition> types) {
    sdl.add(dt);
    for (StructureDefinition sd : types) {
      if (sd.hasBaseDefinition() && sd.getBaseDefinition().equals(dt.getUrl()) && sd.getDerivation() == TypeDerivationRule.SPECIALIZATION) {
        addTypeAndDescendents(sdl, sd, types);
      }
    }  
  }

  private void getClassInfoChildTypesByName(String name, TypeDetails result) {
    if (name.equals("namespace")) {
      result.addType(TypeDetails.FP_String);
    }
    if (name.equals("name")) {
      result.addType(TypeDetails.FP_String);
    }
  }


  private void getSimpleTypeChildTypesByName(String name, TypeDetails result) {
    if (name.equals("namespace")) {
      result.addType(TypeDetails.FP_String);
    }
    if (name.equals("name")) {
      result.addType(TypeDetails.FP_String);
    }
  }


  public List<ElementDefinitionMatch> getElementDefinition(StructureDefinition sd, String path, boolean allowTypedName, ExpressionNode expr) throws PathEngineException {
    for (ElementDefinition ed : sd.getSnapshot().getElement()) {
      if (ed.getPath().equals(path)) {
        if (ed.hasContentReference()) {
          ElementDefinitionMatch res = getElementDefinitionById(sd, ed.getContentReference());
          if (res == null) {
            throw new Error("Unable to find "+ed.getContentReference());
          } else {
            res.sourceDefinition = ed;
          }
          return ml(res);
        } else {
          return ml(new ElementDefinitionMatch(ed, null));
        }
      }
      if (ed.getPath().endsWith("[x]") && path.startsWith(ed.getPath().substring(0, ed.getPath().length()-3)) && path.length() == ed.getPath().length()-3) {
        return ml(new ElementDefinitionMatch(ed, null));
      }
      if (allowTypedName && ed.getPath().endsWith("[x]") && path.startsWith(ed.getPath().substring(0, ed.getPath().length()-3)) && path.length() > ed.getPath().length()-3) {
        String s = Utilities.uncapitalize(path.substring(ed.getPath().length()-3));
        if (primitiveTypes.contains(s)) {
          return ml(new ElementDefinitionMatch(ed, s));
        } else {
          return ml(new ElementDefinitionMatch(ed, path.substring(ed.getPath().length()-3)));
        }
      }
      if (ed.getPath().contains(".") && path.startsWith(ed.getPath()+".") && (ed.getType().size() > 0) && !isAbstractType(ed.getType())) { 
        // now we walk into the type.
        if (ed.getType().size() > 1) { // if there's more than one type, the test above would fail this, but we can get here with CDA
          List<ElementDefinitionMatch> list = new ArrayList<>();
          // for each type, does it have the next node in the path? 
          for (TypeRefComponent tr : ed.getType()) {
            StructureDefinition nsd = worker.fetchResource(StructureDefinition.class, ProfileUtilities.sdNs(tr.getCode(), null), sd);
            if (nsd == null) { 
              throw makeException(expr, I18nConstants.FHIRPATH_NO_TYPE, ed.getType().get(0).getCode(), "getElementDefinition");
            }
            List<ElementDefinitionMatch> edl = getElementDefinition(nsd, nsd.getId()+path.substring(ed.getPath().length()), allowTypedName, expr);
            list.addAll(edl);
          }
          return list;
        }
        StructureDefinition nsd = worker.fetchResource(StructureDefinition.class, ProfileUtilities.sdNs(ed.getType().get(0).getCode(), null), sd);
        if (nsd == null) { 
          throw makeException(expr, I18nConstants.FHIRPATH_NO_TYPE, ed.getType().get(0).getCode(), "getElementDefinition");
        }
        return getElementDefinition(nsd, nsd.getId()+path.substring(ed.getPath().length()), allowTypedName, expr);
      }
      if (ed.hasContentReference() && path.startsWith(ed.getPath()+".")) {
        ElementDefinitionMatch m = getElementDefinitionById(sd, ed.getContentReference());
        if (m == null) {
          throw new Error("Unable to find path "+path+" with a content reference of "+ed.getContentReference());          
        } else {
          List<ElementDefinitionMatch> res = getElementDefinition(sd, m.definition.getPath()+path.substring(ed.getPath().length()), allowTypedName, expr);
          for (ElementDefinitionMatch item : res) {
            item.sourceDefinition = ed;
          }
          return res;
        }
      }
    }
    return ml(null);
  }

  private List<ElementDefinitionMatch> ml(ElementDefinitionMatch item) {
    List<ElementDefinitionMatch> list = new ArrayList<>();
    if (item != null) {
      list.add(item);
    }
    return list;
  }

  private boolean isAbstractType(List<TypeRefComponent> list) {
    if (list.size() != 1) {
      return false;
    } else {
      return isAbstractType(list.get(0).getCode());
    }
  }

  private boolean isAbstractType(String code) {
    StructureDefinition sd = worker.fetchTypeDefinition(code);
    return sd != null && sd.getAbstract() && sd.getKind() != StructureDefinitionKind.RESOURCE;
  }

  
  private boolean hasType(ElementDefinition ed, String s) {
    for (TypeRefComponent t : ed.getType()) {
      if (s.equalsIgnoreCase(t.getCode())) {
        return true;
      }
    }
    return false;
  }

  private boolean hasDataType(ElementDefinition ed) {
    return ed.hasType() && !(ed.getType().get(0).getCode().equals("Element") || ed.getType().get(0).getCode().equals("BackboneElement") || isAbstractType(ed.getType().get(0).getCode()));
  }

  private ElementDefinitionMatch getElementDefinitionById(StructureDefinition sd, String ref) {
    StructureDefinition sdt = sd; 
    while (sdt != null) {
      if (ref.startsWith(sdt.getUrl()+"#")) {
        ref = ref.replace(sdt.getUrl()+"#", "#");
        break;
      }
      sdt = worker.fetchResource(StructureDefinition.class, sdt.getBaseDefinition());
    }
    for (ElementDefinition ed : sd.getSnapshot().getElement()) {
      if (ref.equals("#"+ed.getId())) {
        return new ElementDefinitionMatch(ed, null);
      }
    }
    return null;
  }


  public boolean hasLog() {
    return log != null && log.length() > 0;
  }


  public String takeLog() {
    if (!hasLog()) {
      return "";
    }
    String s = log.toString();
    log = new StringBuilder();
    return s;
  }


  /** given an element definition in a profile, what element contains the differentiating fixed 
   * for the element, given the differentiating expression. The expression is only allowed to 
   * use a subset of FHIRPath
   * 
   * @param profile
   * @param element
   * @return
   * @throws PathEngineException 
   * @throws DefinitionException 
   */
  public TypedElementDefinition evaluateDefinition(ExpressionNode expr, StructureDefinition profile, TypedElementDefinition element, StructureDefinition source, boolean dontWalkIntoReferences) throws DefinitionException {
    StructureDefinition sd = profile;
    TypedElementDefinition focus = null;
    boolean okToNotResolve = false;

    if (expr.getKind() == Kind.Name) {
      if (element.getElement().hasSlicing()) {
        ElementDefinition slice = pickMandatorySlice(sd, element.getElement());
        if (slice == null) {
          throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_NAME_ALREADY_SLICED, element.getElement().getId());
        }
        element = new TypedElementDefinition(slice);
      }

      if (expr.getName().equals("$this")) {
        focus = element;
      } else { 
        SourcedChildDefinitions childDefinitions;
        childDefinitions = profileUtilities.getChildMap(sd, element.getElement(), false);
        // if that's empty, get the children of the type
        if (childDefinitions.getList().isEmpty()) {

          sd = fetchStructureByType(element, expr);
          if (sd == null) {
            throw makeException(expr, I18nConstants.FHIRPATH_RESOLVE_DISCRIMINATOR_CANT_FIND, element.getElement().getType().get(0).getProfile(), element.getElement().getId());
          }
          childDefinitions = profileUtilities.getChildMap(sd, sd.getSnapshot().getElementFirstRep(), false);
        }
        for (ElementDefinition t : childDefinitions.getList()) {
          if (tailMatches(t, expr.getName()) && !t.hasSlicing()) { // GG: slicing is a problem here. This is for an exetnsion with a fixed value (type slicing) 
            focus = new TypedElementDefinition(t);
            break;
          }
        }
      }
    } else if (expr.getKind() == Kind.Function) {
      if ("resolve".equals(expr.getName())) {
        if (element.getTypes().size() == 0) {
          throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_RESOLVE_NO_TYPE, element.getElement().getId());
        }
        if (element.getTypes().size() > 1) {
          throw makeExceptionPlural(element.getTypes().size(), expr, I18nConstants.FHIRPATH_DISCRIMINATOR_RESOLVE_MULTIPLE_TYPES, element.getElement().getId());
        }
        if (!element.getTypes().get(0).hasTarget()) {
          throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_RESOLVE_NOT_REFERENCE, element.getElement().getId(), element.getElement().getType().get(0).getCode()+")");
        }
        if (element.getTypes().get(0).getTargetProfile().size() > 1) {
          throw makeExceptionPlural(element.getTypes().get(0).getTargetProfile().size(), expr, I18nConstants.FHIRPATH_RESOLVE_DISCRIMINATOR_NO_TARGET, element.getElement().getId());
        }
        sd = worker.fetchResource(StructureDefinition.class, element.getTypes().get(0).getTargetProfile().get(0).getValue(), profile);
        if (sd == null) {
          throw makeException(expr, I18nConstants.FHIRPATH_RESOLVE_DISCRIMINATOR_CANT_FIND, element.getTypes().get(0).getTargetProfile(), element.getElement().getId());
        }
        focus = new TypedElementDefinition(sd.getSnapshot().getElementFirstRep());
      } else if ("extension".equals(expr.getName())) {
        String targetUrl = expr.getParameters().get(0).getConstant().primitiveValue();
        SourcedChildDefinitions childDefinitions = profileUtilities.getChildMap(sd, element.getElement(), true);
        for (ElementDefinition t : childDefinitions.getList()) {
          if (t.getPath().endsWith(".extension") && t.hasSliceName()) {
            StructureDefinition exsd = (t.getType() == null || t.getType().isEmpty() || t.getType().get(0).getProfile().isEmpty()) ?
                null : worker.fetchResource(StructureDefinition.class, t.getType().get(0).getProfile().get(0).getValue(), profile);
            while (exsd != null && !exsd.getBaseDefinition().equals("http://hl7.org/fhir/StructureDefinition/Extension")) {
              exsd = worker.fetchResource(StructureDefinition.class, exsd.getBaseDefinition(), exsd);
            }
            if (exsd != null && exsd.getUrl().equals(targetUrl)) {
              if (profileUtilities.getChildMap(sd, t, false).getList().isEmpty()) {
                sd = exsd;
              }
              focus = new TypedElementDefinition(t);
              break;
            }
          }
        }
        if (focus == null) { 
          throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_CANT_FIND_EXTENSION, expr.toString(), targetUrl, element.getElement().getId(), sd.getUrl());
        }
      } else if ("ofType".equals(expr.getName())) {
        if (!element.getElement().hasType()) {
          throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_TYPE_NONE, element.getElement().getId());
        }
        List<String> atn = new ArrayList<>();
        for (TypeRefComponent tr : element.getTypes()) {
          if (!tr.hasCode()) {
            throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_NO_CODE, element.getElement().getId());
          }
          atn.add(tr.getCode());
        }
        String stn = expr.getParameters().get(0).getName();  
        okToNotResolve = true;
        if ((atn.contains(stn))) {
          if (element.getTypes().size() > 1) {
            focus = new TypedElementDefinition( element.getSrc(), element.getElement(), stn);
          } else {
            focus = element;
          }
        }
      } else {
        throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_BAD_NAME, expr.getName());
      }
    } else if (expr.getKind() == Kind.Group) {
      throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_BAD_SYNTAX_GROUP, expr.toString());
    } else if (expr.getKind() == Kind.Constant) {
      throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_BAD_SYNTAX_CONST);
    }

    if (focus == null) { 
      if (okToNotResolve) {
        return null;
      } else {
        throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_CANT_FIND, expr.toString(), source.getUrl(), element.getElement().getId(), profile.getUrl());
      }
    } else {
      // gdg 26-02-2022. If we're walking towards a resolve() and we're on a reference, and  we try to walk into the reference
      // then we don't do that. .resolve() is allowed on the Reference.reference, but the target of the reference will be defined
      // on the Reference, not the reference.reference.
      ExpressionNode next = expr.getInner();
      if (dontWalkIntoReferences && focus.hasType("Reference") && next != null && next.getKind() == Kind.Name && next.getName().equals("reference")) {
        next = next.getInner();
      }
      if (next == null) {
        return focus;
      } else {
        return evaluateDefinition(next, sd, focus, profile, dontWalkIntoReferences);
      }
    }
  }

  private ElementDefinition pickMandatorySlice(StructureDefinition sd, ElementDefinition element) throws DefinitionException {
    List<ElementDefinition> list = profileUtilities.getSliceList(sd, element);
    for (ElementDefinition ed : list) {
      if (ed.getMin() > 0) {
        return ed;
      }
    }
    return null;
  }


  private StructureDefinition fetchStructureByType(TypedElementDefinition ed, ExpressionNode expr) throws DefinitionException {
    if (ed.getTypes().size() == 0) {
      throw makeException(expr, I18nConstants.FHIRPATH_DISCRIMINATOR_NOTYPE, ed.getElement().getId());
    }
    if (ed.getTypes().size() > 1) {
      throw makeExceptionPlural(ed.getTypes().size(), expr, I18nConstants.FHIRPATH_DISCRIMINATOR_MULTIPLE_TYPES, ed.getElement().getId());
    }
    if (ed.getTypes().get(0).getProfile().size() > 1) {
      throw makeExceptionPlural(ed.getTypes().get(0).getProfile().size(), expr, I18nConstants.FHIRPATH_DISCRIMINATOR_MULTIPLE_PROFILES, ed.getElement().getId());
    }
    if (ed.getTypes().get(0).hasProfile()) { 
      return worker.fetchResource(StructureDefinition.class, ed.getTypes().get(0).getProfile().get(0).getValue(), ed.getSrc());
    } else {
      return worker.fetchResource(StructureDefinition.class, ProfileUtilities.sdNs(ed.getTypes().get(0).getCode(), null), ed.getSrc());
    }
  }


  private boolean tailMatches(ElementDefinition t, String d) {
    String tail = tailDot(t.getPath());
    if (d.contains("[")) {
      return tail.startsWith(d.substring(0, d.indexOf('[')));
    } else if (tail.equals(d)) {
      return true;
    } else if (t.getType().size() == 1 && t.getType().get(0).getCode() != null && t.getPath() != null && t.getPath().toUpperCase().endsWith(t.getType().get(0).getCode().toUpperCase())) {
      return tail.startsWith(d);
    } else if (t.getPath().endsWith("[x]") && tail.startsWith(d)) {
      return true;
    }
    return false;
  }

  private String tailDot(String path) {
    return path.substring(path.lastIndexOf(".") + 1);
  }

  private Equality asBool(List<Base> items, ExpressionNode expr) throws PathEngineException {
    if (items.size() == 0) {
      return Equality.Null;
    } else if (items.size() == 1 && items.get(0).isBooleanPrimitive()) {
      return asBool(items.get(0), true);
    } else if (items.size() == 1) {
      return Equality.True; 
    } else {
      throw makeException(expr, I18nConstants.FHIRPATH_UNABLE_BOOLEAN, convertToString(items));
    }
  }

  private Equality asBoolFromInt(String s) {
    try {
      int i = Integer.parseInt(s);
      switch (i) {
      case 0: return Equality.False;
      case 1: return Equality.True;
      default: return Equality.Null;
      }
    } catch (Exception e) {
      return Equality.Null;
    }
  }

  private Equality asBoolFromDec(String s) {
    try {
      BigDecimal d = new BigDecimal(s);
      if (d.compareTo(BigDecimal.ZERO) == 0) { 
        return Equality.False;
      } else if (d.compareTo(BigDecimal.ONE) == 0) { 
        return Equality.True;
      } else {
        return Equality.Null;
      }
    } catch (Exception e) {
      return Equality.Null;
    }
  }

  private Equality asBool(Base item, boolean narrow) {
    if (item instanceof BooleanType) { 
      return boolToTriState(((BooleanType) item).booleanValue());
    } else if (item.isBooleanPrimitive()) {
      if (Utilities.existsInList(item.primitiveValue(), "true")) {
        return Equality.True;
      } else if (Utilities.existsInList(item.primitiveValue(), "false")) {
        return Equality.False;
      } else { 
        return Equality.Null;
      }
    } else if (narrow) {
      return Equality.False;
    } else if (item instanceof IntegerType || Utilities.existsInList(item.fhirType(), "integer", "positiveint", "unsignedInt")) {
      return asBoolFromInt(item.primitiveValue());
    } else if (item instanceof DecimalType || Utilities.existsInList(item.fhirType(), "decimal")) {
      return asBoolFromDec(item.primitiveValue());
    } else if (Utilities.existsInList(item.fhirType(), FHIR_TYPES_STRING)) {
      if (Utilities.existsInList(item.primitiveValue(), "true", "t", "yes", "y")) {
        return Equality.True;
      } else if (Utilities.existsInList(item.primitiveValue(), "false", "f", "no", "n")) {
        return Equality.False;
      } else if (Utilities.isInteger(item.primitiveValue())) {
        return asBoolFromInt(item.primitiveValue());
      } else if (Utilities.isDecimal(item.primitiveValue(), true)) {
        return asBoolFromDec(item.primitiveValue());
      } else {
        return Equality.Null;
      }
    } 
    return Equality.Null;
  }

  private Equality boolToTriState(boolean b) {
    return b ? Equality.True : Equality.False;
  }


  public ValidationOptions getTerminologyServiceOptions() {
    return terminologyServiceOptions;
  }


  public IWorkerContext getWorker() {
    return worker;
  }

  public boolean isAllowPolymorphicNames() {
    return allowPolymorphicNames;
  }

  public void setAllowPolymorphicNames(boolean allowPolymorphicNames) {
    this.allowPolymorphicNames = allowPolymorphicNames;
  }

  public boolean isLiquidMode() {
    return liquidMode;
  }

  public void setLiquidMode(boolean liquidMode) {
    this.liquidMode = liquidMode;
  }

  public ProfileUtilities getProfileUtilities() {
    return profileUtilities;
  }

  public boolean isAllowDoubleQuotes() {
    return allowDoubleQuotes;
  }
  public void setAllowDoubleQuotes(boolean allowDoubleQuotes) {
    this.allowDoubleQuotes = allowDoubleQuotes;    
  }

  public boolean isEmitSQLonFHIRWarning() {
    return emitSQLonFHIRWarning;
  }

  public void setEmitSQLonFHIRWarning(boolean emitSQLonFHIRWarning) {
    this.emitSQLonFHIRWarning = emitSQLonFHIRWarning;
  }
  
}