package org.hl7.fhir.dstu3.fhirpath;

import java.math.BigDecimal;
import java.util.ArrayList;
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 org.fhir.ucum.Decimal;
import org.fhir.ucum.UcumException;
import org.hl7.fhir.dstu3.context.IWorkerContext;
import org.hl7.fhir.dstu3.fhirpath.ExpressionNode.CollectionStatus;
import org.hl7.fhir.dstu3.fhirpath.ExpressionNode.Function;
import org.hl7.fhir.dstu3.fhirpath.ExpressionNode.Kind;
import org.hl7.fhir.dstu3.fhirpath.ExpressionNode.Operation;
import org.hl7.fhir.dstu3.fhirpath.ExpressionNode.SourceLocation;
import org.hl7.fhir.dstu3.fhirpath.FHIRLexer.FHIRLexerException;
import org.hl7.fhir.dstu3.fhirpath.FHIRPathUtilityClasses.ExecutionContext;
import org.hl7.fhir.dstu3.fhirpath.FHIRPathUtilityClasses.ExecutionTypeContext;
import org.hl7.fhir.dstu3.fhirpath.FHIRPathUtilityClasses.FunctionDetails;
import org.hl7.fhir.dstu3.fhirpath.TypeDetails.ProfiledType;
import org.hl7.fhir.dstu3.model.Base;
import org.hl7.fhir.dstu3.model.BooleanType;
import org.hl7.fhir.dstu3.model.DateTimeType;
import org.hl7.fhir.dstu3.model.DateType;
import org.hl7.fhir.dstu3.model.DecimalType;
import org.hl7.fhir.dstu3.model.ElementDefinition;
import org.hl7.fhir.dstu3.model.ElementDefinition.TypeRefComponent;
import org.hl7.fhir.dstu3.model.IntegerType;
import org.hl7.fhir.dstu3.model.Property;
import org.hl7.fhir.dstu3.model.Resource;
import org.hl7.fhir.dstu3.model.StringType;
import org.hl7.fhir.dstu3.model.StructureDefinition;
import org.hl7.fhir.dstu3.model.StructureDefinition.StructureDefinitionKind;
import org.hl7.fhir.dstu3.model.StructureDefinition.TypeDerivationRule;
import org.hl7.fhir.dstu3.model.TimeType;
import org.hl7.fhir.exceptions.DefinitionException;
import org.hl7.fhir.exceptions.FHIRException;
import org.hl7.fhir.exceptions.PathEngineException;
import org.hl7.fhir.utilities.Utilities;

/*
  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.
  
 */



import ca.uhn.fhir.model.api.TemporalPrecisionEnum;
import ca.uhn.fhir.rest.server.exceptions.InternalErrorException;
import ca.uhn.fhir.util.ElementUtil;

/**
 *
 * @author Grahame Grieve
 *
 */
public class FHIRPathEngine {
  private IWorkerContext worker;
  private IEvaluationContext hostServices;
  private StringBuilder log = new StringBuilder();
  private Set<String> primitiveTypes = new HashSet<String>();
  private Map<String, StructureDefinition> allTypes = new HashMap<String, StructureDefinition>();

  // if the fhir path expressions are allowed to use constants beyond those defined in the specification
  // the application can implement them by providing a constant resolver
  public interface IEvaluationContext {
   

    /**
     * A constant reference - e.g. a reference to a name that must be resolved in context.
     * The % will be removed from the constant name before this is invoked.
     *
     * This will also be called if the host invokes the FluentPath engine with a context of null
     *
     * @param appContext - content passed into the fluent path engine
     * @param name - name reference to resolve
     * @return the value of the reference (or null, if it's not valid, though can throw an exception if desired)
     */
    public Base resolveConstant(Object appContext, String name)  throws PathEngineException;
    public TypeDetails resolveConstantType(Object appContext, String name) throws PathEngineException;

    /**
     * when the .log() function is called
     *
     * @param argument
     * @param focus
     * @return
     */
    public boolean log(String argument, List<Base> focus);

    // extensibility for functions
    /**
     *
     * @param functionName
     * @return null if the function is not known
     */
    public FunctionDetails resolveFunction(String functionName);

    /**
     * Check the function parameters, and throw an error if they are incorrect, or return the type for the function
     * @param functionName
     * @param parameters
     * @return
     */
    public TypeDetails checkFunction(Object appContext, String functionName, List<TypeDetails> parameters) throws PathEngineException;

    /**
     * @param appContext
     * @param functionName
     * @param parameters
     * @return
     */
    public List<Base> executeFunction(Object appContext, String functionName, List<List<Base>> parameters);

    /**
     * Implementation of resolve() function. Passed a string, return matching resource, if one is known - else null
     * @param url
     * @return
     */
    public Base resolveReference(Object appContext, String url);
  }


  /**
   * @param worker - used when validating paths (@check), and used doing value set membership when executing tests (once that's defined)
   */
  public FHIRPathEngine(IWorkerContext worker) {
    super();
    this.worker = worker;
    for (StructureDefinition sd : worker.allStructures()) {
      if (sd.getDerivation() == TypeDerivationRule.SPECIALIZATION)
        allTypes.put(sd.getName(), sd);
      if (sd.getDerivation() == TypeDerivationRule.SPECIALIZATION && sd.getKind() == StructureDefinitionKind.PRIMITIVETYPE) {
        primitiveTypes.add(sd.getName());
      }
    }
  }


  // --- 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 IEvaluationContext getHostServices() {
    return hostServices;
  }


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


  /**
   * 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 {
        Base[] list = item.listChildrenByName(name, false);
        if (list != null)
                for (Base v : list)
      if (v != null)
        result.add(v);
  }

  // --- public API -------------------------------------------------------
  /**
   * Parse a path for later use using execute
   *
   * @param path
   * @return
   * @throws PathEngineException
   * @throws Exception
   */
  public ExpressionNode parse(String path) throws FHIRLexerException {
    FHIRLexer lexer = new FHIRLexer(path);
    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;
  }

  /**
   * 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 resourceType, 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 == 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.fetchResource(StructureDefinition.class, 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 = worker.fetchResource(StructureDefinition.class, ctxt);
          if (sd == null)
            throw new PathEngineException("Unknown context "+context);
          ElementDefinitionMatch ed = getElementDefinition(sd, context, true);
          if (ed == null)
            throw new PathEngineException("Unknown context element "+context);
          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, resourceType, context, types), types, expr, true);
  }

  public TypeDetails check(Object appContext, 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 {
      ElementDefinitionMatch ed = getElementDefinition(sd, context, true);
      if (ed == null)
        throw new PathEngineException("Unknown context element "+context);
      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, sd.getUrl(), context, types), types, expr, true);
  }

  public TypeDetails check(Object appContext, 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, sd == null ? null : sd.getUrl(), null, types), types, expr, true);
  }

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


  /**
   * 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), 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, null, 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 resource, 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, resource, base, null, 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 resource, 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, resource, base, null, 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 resource, 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, resource, base, null, 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 resource, Base base, String path) throws FHIRException {
    return convertToBoolean(evaluate(null, resource, 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 resource, Base base, ExpressionNode node) throws FHIRException {
    return convertToBoolean(evaluate(null, resource, 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, Resource resource, Base base, ExpressionNode node) throws FHIRException {
    return convertToBoolean(evaluate(appInfo, resource, 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(Base resource, Base base, ExpressionNode node) throws FHIRException {
    return convertToBoolean(evaluate(null, resource, 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 resource, Base base, ExpressionNode node) throws FHIRException {
    return convertToString(evaluate(appInfo, resource, 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();
  }

  private String convertToString(Base item) {
    if (item.isPrimitive())
      return item.primitiveValue();
    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
      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 "";
  }

  private ExpressionNode parseExpression(FHIRLexer lexer, boolean proximal) throws FHIRLexerException {
    ExpressionNode result = new ExpressionNode(lexer.nextId());
    SourceLocation c = lexer.getCurrentStartLocation();
    result.setStart(lexer.getCurrentLocation());
    // special:
    if (lexer.getCurrent().equals("-")) {
      lexer.take();
      lexer.setCurrent("-"+lexer.getCurrent());
    }
    if (lexer.getCurrent().equals("+")) {
      lexer.take();
      lexer.setCurrent("+"+lexer.getCurrent());
    }
    if (lexer.isConstant(false)) {
      checkConstant(lexer.getCurrent(), lexer);
      result.setConstant(lexer.take());
      result.setKind(Kind.Constant);
      result.setEnd(lexer.getCurrentLocation());
    } 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());
      lexer.next();
    } else {
      if (!lexer.isToken() && !lexer.getCurrent().startsWith("\""))
        throw lexer.error("Found "+lexer.getCurrent()+" expecting a token name");
      if (lexer.getCurrent().startsWith("\""))
        result.setName(lexer.readConstant("Path Name"));
      else
        result.setName(lexer.take());
      result.setEnd(lexer.getCurrentLocation());
      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(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");
        }
        result.setEnd(lexer.getCurrentLocation());
        lexer.next();
        checkParameters(lexer, c, result, details);
      } else
        result.setKind(Kind.Name);
    }
    ExpressionNode focus = result;
    if ("[".equals(lexer.getCurrent())) {
      lexer.next();
      ExpressionNode item = new ExpressionNode(lexer.nextId());
      item.setKind(Kind.Function);
      item.setFunction(ExpressionNode.Function.Item);
      item.getParameters().add(parseExpression(lexer, true));
      if (!lexer.getCurrent().equals("]"))
        throw lexer.error("The token "+lexer.getCurrent()+" is not expected here - a \"]\" expected");
      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());
        focus.setOpEnd(lexer.getCurrentLocation());
        lexer.next();
        focus.setOpNext(parseExpression(lexer, false));
        focus = focus.getOpNext();
      }
      result = organisePrecedence(lexer, result);
    }
    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.LessThen, Operation.Greater, Operation.LessOrEqual, Operation.GreaterOrEqual));
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Is));
    node = gatherPrecedence(lexer, node, EnumSet.of(Operation.Equals, Operation.Equivalent, Operation.NotEquals, Operation.NotEquivalent));
    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());
        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 void checkConstant(String s, FHIRLexer lexer) throws FHIRLexerException {
    if (s.startsWith("\'") && s.endsWith("\'")) {
      int i = 1;
      while (i < s.length()-1) {
        char ch = s.charAt(i);
        if (ch == '\\') {
          switch (ch) {
          case 't':
          case 'r':
          case 'n':
          case 'f':
          case '\'':
          case '\\':
          case '/':
            i++;
            break;
          case 'u':
            if (!Utilities.isHex("0x"+s.substring(i, i+4)))
              throw lexer.error("Improper unicode escape \\u"+s.substring(i, i+4));
            break;
          default:
            throw lexer.error("Unknown character escape \\"+ch);
          }
        } else
          i++;
      }
    }
  }

  //  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());
    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());
    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);
    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 Item: return checkParamCount(lexer, location, exp, 1);
    case As: return checkParamCount(lexer, location, exp, 1);
    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 Iif: return checkParamCount(lexer, location, exp, 2,3);
    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 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 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);
    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 HasValue: return checkParamCount(lexer, location, exp, 0);
    case Alias: return checkParamCount(lexer, location, exp, 1);
    case AliasAs: return checkParamCount(lexer, location, exp, 1);
    case Custom: return checkParamCount(lexer, location, exp, details.getMinParameters(), details.getMaxParameters());
    }
    return false;
  }

        private List<Base> execute(ExecutionContext context, List<Base> focus, ExpressionNode exp, boolean atEntry) throws FHIRException {
//    System.out.println("Evaluate {'"+exp.toString()+"'} on "+focus.toString());
    List<Base> work = new ArrayList<Base>();
    switch (exp.getKind()) {
    case Name:
      if (atEntry && exp.getName().equals("$this"))
        work.add(context.getThisItem());
      else
        for (Base item : focus) {
          List<Base> outcome = execute(context, item, exp, atEntry);
          for (Base base : outcome)
            if (base != null)
              work.add(base);
        }
      break;
    case Function:
      List<Base> work2 = evaluateFunction(context, focus, exp);
      work.addAll(work2);
      break;
    case Constant:
      Base b = processConstant(context, exp.getConstant());
      if (b != null)
        work.add(b);
      break;
    case Group:
      work2 = execute(context, focus, exp.getGroup(), atEntry);
      work.addAll(work2);
    }

    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) {
        List<Base> work2 = preOperate(work, last.getOperation());
        if (work2 != null)
          work = work2;
        else if (last.getOperation() == Operation.Is || last.getOperation() == Operation.As) {
          work2 = executeTypeName(context, focus, next, false);
          work = operate(work, last.getOperation(), work2);
        } else {
          work2 = execute(context, focus, next, true);
          work = operate(work, last.getOperation(), work2);
//          System.out.println("Result of {'"+last.toString()+" "+last.getOperation().toCode()+" "+next.toString()+"'}: "+focus.toString());
        }
        last = next;
        next = next.getOpNext();
      }
    }
//    System.out.println("Result of {'"+exp.toString()+"'}: "+work.toString());
    return work;
  }

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


  private List<Base> preOperate(List<Base> left, Operation operation) {
    switch (operation) {
    case And:
      return isBoolean(left, false) ? makeBoolean(false) : null;
    case Or:
      return isBoolean(left, true) ? makeBoolean(true) : null;
    case Implies:
      return convertToBoolean(left) ? null : makeBoolean(true);
    default:
      return null;
    }
  }

  private List<Base> makeBoolean(boolean b) {
    List<Base> res = new ArrayList<Base>();
    res.add(new BooleanType(b));
    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 context, TypeDetails focus, ExpressionNode exp, boolean atEntry) throws PathEngineException, DefinitionException {
    TypeDetails result = new TypeDetails(null);
    switch (exp.getKind()) {
    case Name:
      if (atEntry && exp.getName().equals("$this"))
        result.update(context.getThisItem());
      else if (atEntry && focus == null)
        result.update(executeContextType(context, exp.getName()));
      else {
        for (String s : focus.getTypes()) {
          result.update(executeType(s, exp, atEntry));
        }
        if (result.hasNoTypes())
          throw new PathEngineException("The name "+exp.getName()+" is not valid for any of the possible types: "+focus.describe());
      }
      break;
    case Function:
      result.update(evaluateFunctionType(context, focus, exp));
      break;
    case Constant:
      result.update(readConstantType(context, exp.getConstant()));
      break;
    case Group:
      result.update(executeType(context, focus, exp.getGroup(), atEntry));
    }
    exp.setTypes(result);

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

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

  private Base processConstant(ExecutionContext context, String constant) throws PathEngineException {
    if (constant.equals("true")) {
      return new BooleanType(true);
    } else if (constant.equals("false")) {
      return new BooleanType(false);
    } else if (constant.equals("{}")) {
      return null;
    } else if (Utilities.isInteger(constant)) {
      return new IntegerType(constant);
    } else if (Utilities.isDecimal(constant, false)) {
      return new DecimalType(constant);
    } else if (constant.startsWith("\'")) {
      return new StringType(processConstantString(constant));
    } else if (constant.startsWith("%")) {
      return resolveConstant(context, constant);
    } else if (constant.startsWith("@")) {
      return processDateConstant(context.getAppInfo(), constant.substring(1));
    } else {
      return new StringType(constant);
    }
  }

  private Base processDateConstant(Object appInfo, String value) throws PathEngineException {
    if (value.startsWith("T"))
      return new TimeType(value.substring(1));
    String v = value;
    if (v.length() > 10) {
      int i = v.substring(10).indexOf("-");
      if (i == -1)
        i = v.substring(10).indexOf("+");
      if (i == -1)
        i = v.substring(10).indexOf("Z");
      v = i == -1 ? value : v.substring(0,  10+i);
    }
    if (v.length() > 10)
      return new DateTimeType(value);
    else
      return new DateType(value);
  }


  private Base resolveConstant(ExecutionContext context, String s) throws PathEngineException {
    if (s.equals("%sct"))
      return new StringType("http://snomed.info/sct");
    else if (s.equals("%loinc"))
      return new StringType("http://loinc.org");
    else if (s.equals("%ucum"))
      return new StringType("http://unitsofmeasure.org");
    else if (s.equals("%resource")) {
      if (context.getResource() == null)
        throw new PathEngineException("Cannot use %resource in this context");
      return context.getResource();
    } else if (s.equals("%context")) {
      return context.getContext();
    } else if (s.equals("%us-zip"))
      return new StringType("[0-9]{5}(-[0-9]{4}){0,1}");
    else if (s.startsWith("%\"vs-"))
      return new StringType("http://hl7.org/fhir/ValueSet/"+s.substring(5, s.length()-1)+"");
    else if (s.startsWith("%\"cs-"))
      return new StringType("http://hl7.org/fhir/"+s.substring(5, s.length()-1)+"");
    else if (s.startsWith("%\"ext-"))
      return new StringType("http://hl7.org/fhir/StructureDefinition/"+s.substring(6, s.length()-1));
    else if (hostServices == null)
      throw new PathEngineException("Unknown fixed constant '"+s+"'");
    else
      return hostServices.resolveConstant(context.getAppInfo(), s.substring(1));
  }


  private String processConstantString(String s) throws PathEngineException {
    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 'u':
          i++;
          int uc = Integer.parseInt(s.substring(i, i+4), 16);
          b.append((char) uc);
          i = i + 3;
          break;
        default:
          throw new PathEngineException("Unknown character escape \\"+s.charAt(i));
        }
        i++;
      } else {
        b.append(ch);
        i++;
      }
    }
    return b.toString();
  }


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

  private List<Base> opAs(List<Base> left, List<Base> right) {
    List<Base> result = new ArrayList<Base>();
    if (left.size() != 1 || right.size() != 1)
      return result;
    else {
      String tn = convertToString(right);
      if (tn.equals(left.get(0).fhirType()))
        result.add(left.get(0));
    }
    return result;
  }


  private List<Base> opIs(List<Base> left, List<Base> right) {
    List<Base> result = new ArrayList<Base>();
    if (left.size() != 1 || right.size() != 1)
      result.add(new BooleanType(false));
    else {
      String tn = convertToString(right);
      result.add(new BooleanType(left.get(0).hasType(tn)));
    }
    return result;
  }


  private TypeDetails operateTypes(TypeDetails left, Operation operation, TypeDetails right) {
    switch (operation) {
    case Equals: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Equivalent: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case NotEquals: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case NotEquivalent: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case LessThen: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Greater: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case LessOrEqual: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case GreaterOrEqual: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Is: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case As: return new TypeDetails(CollectionStatus.SINGLETON, right.getTypes());
    case Union: return left.union(right);
    case Or: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case And: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Xor: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Implies : return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Times:
      TypeDetails result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer"))
        result.addType("integer");
      else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal"))
        result.addType("decimal");
      return result;
    case DivideBy:
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer"))
        result.addType("decimal");
      else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal"))
        result.addType("decimal");
      return result;
    case Concatenate:
      result = new TypeDetails(CollectionStatus.SINGLETON, "");
      return result;
    case Plus:
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer"))
        result.addType("integer");
      else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal"))
        result.addType("decimal");
      else if (left.hasType(worker, "string", "id", "code", "uri") && right.hasType(worker, "string", "id", "code", "uri"))
        result.addType("string");
      return result;
    case Minus:
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer"))
        result.addType("integer");
      else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal"))
        result.addType("decimal");
      return result;
    case Div:
    case Mod:
      result = new TypeDetails(CollectionStatus.SINGLETON);
      if (left.hasType(worker, "integer") && right.hasType(worker, "integer"))
        result.addType("integer");
      else if (left.hasType(worker, "integer", "decimal") && right.hasType(worker, "integer", "decimal"))
        result.addType("decimal");
      return result;
    case In: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Contains: return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    default:
      return null;
    }
  }


  private List<Base> opEquals(List<Base> left, List<Base> right) {
    if (left.size() != right.size())
      return makeBoolean(false);

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

  private List<Base> opNotEquals(List<Base> left, List<Base> right) {
    if (left.size() != right.size())
      return makeBoolean(true);

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

  private boolean doEquals(Base left, Base right) {
    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 {
    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"))
      return Utilities.equivalentNumber(left.primitiveValue(), right.primitiveValue());
    if (left.hasType("string", "id", "code", "uri") && right.hasType("string", "id", "code", "uri"))
      return Utilities.equivalent(convertToString(left), convertToString(right));

    throw new PathEngineException(String.format("Unable to determine equivalence between %s and %s", left.fhirType(), right.fhirType()));
  }

  private List<Base> opEquivalent(List<Base> left, List<Base> right) 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) 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 List<Base> opLessThen(List<Base> left, List<Base> right) throws FHIRException {
    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("string") && r.hasType("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")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) < 0);
      else if ((l.hasType("time")) && (r.hasType("time")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) < 0);
    } 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 opLessThen(left.get(0).listChildrenByName("value"), right.get(0).listChildrenByName("value"));
      } else {
                                throw new InternalErrorException("Canonical Comparison isn't done yet");
      }
    }
    return new ArrayList<Base>();
  }

        private List<Base> opGreater(List<Base> left, List<Base> right) throws FHIRException {
    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("string") && r.hasType("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")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) > 0);
      else if ((l.hasType("time")) && (r.hasType("time")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) > 0);
    } 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"));
      } else {
                                throw new InternalErrorException("Canonical Comparison isn't done yet");
      }
    }
    return new ArrayList<Base>();
  }

        private List<Base> opLessOrEqual(List<Base> left, List<Base> right) throws FHIRException {
    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("string") && r.hasType("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")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) <= 0);
      else if ((l.hasType("time")) && (r.hasType("time")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) <= 0);
    } 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"));
      } else {
                                throw new InternalErrorException("Canonical Comparison isn't done yet");
      }
    }
    return new ArrayList<Base>();
  }

        private List<Base> opGreaterOrEqual(List<Base> left, List<Base> right) throws FHIRException {
    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("string") && r.hasType("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")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) >= 0);
      else if ((l.hasType("time")) && (r.hasType("time")))
        return makeBoolean(l.primitiveValue().compareTo(r.primitiveValue()) >= 0);
    } 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"));
      } else {
                                throw new InternalErrorException("Canonical Comparison isn't done yet");
      }
    }
    return new ArrayList<Base>();
  }

  private List<Base> opIn(List<Base> left, List<Base> right) {
    boolean ans = true;
    for (Base l : left) {
      boolean f = false;
      for (Base r : right)
        if (doEquals(l, r)) {
          f = true;
          break;
        }
      if (!f) {
        ans = false;
        break;
      }
    }
    return makeBoolean(ans);
  }

  private List<Base> opContains(List<Base> left, List<Base> right) {
    boolean ans = true;
    for (Base r : right) {
      boolean f = false;
      for (Base l : left)
        if (doEquals(l, r)) {
          f = true;
          break;
        }
      if (!f) {
        ans = false;
        break;
      }
    }
    return makeBoolean(ans);
  }

  private List<Base> opPlus(List<Base> left, List<Base> right) throws PathEngineException {
    if (left.size() == 0)
      throw new PathEngineException("Error performing +: left operand has no value");
    if (left.size() > 1)
      throw new PathEngineException("Error performing +: left operand has more than one value");
    if (!left.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing +: left operand has the wrong type (%s)", left.get(0).fhirType()));
    if (right.size() == 0)
      throw new PathEngineException("Error performing +: right operand has no value");
    if (right.size() > 1)
      throw new PathEngineException("Error performing +: right operand has more than one value");
    if (!right.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing +: right operand has the wrong type (%s)", right.get(0).fhirType()));

    List<Base> result = new ArrayList<Base>();
    Base l = left.get(0);
    Base r = right.get(0);
    if (l.hasType("string", "id", "code", "uri") && r.hasType("string", "id", "code", "uri"))
      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
      throw new PathEngineException(String.format("Error performing +: left and right operand have incompatible or illegal types (%s, %s)", left.get(0).fhirType(), right.get(0).fhirType()));
    return result;
  }

  private List<Base> opTimes(List<Base> left, List<Base> right) throws PathEngineException {
    if (left.size() == 0)
      throw new PathEngineException("Error performing *: left operand has no value");
    if (left.size() > 1)
      throw new PathEngineException("Error performing *: left operand has more than one value");
    if (!left.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing +: left operand has the wrong type (%s)", left.get(0).fhirType()));
    if (right.size() == 0)
      throw new PathEngineException("Error performing *: right operand has no value");
    if (right.size() > 1)
      throw new PathEngineException("Error performing *: right operand has more than one value");
    if (!right.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing *: right operand has the wrong type (%s)", 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
      throw new PathEngineException(String.format("Error performing *: left and right operand have incompatible or illegal types (%s, %s)", left.get(0).fhirType(), right.get(0).fhirType()));
    return result;
  }

  private List<Base> opConcatenate(List<Base> left, List<Base> right) {
    List<Base> result = new ArrayList<Base>();
    result.add(new StringType(convertToString(left) + convertToString((right))));
    return result;
  }

  private List<Base> opUnion(List<Base> left, List<Base> right) {
    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)
      if (doEquals(test, item))
        return true;
    return false;
  }


  private List<Base> opAnd(List<Base> left, List<Base> right) {
    if (left.isEmpty() && right.isEmpty())
      return new ArrayList<Base>();
    else if (isBoolean(left, false) || isBoolean(right, false))
      return makeBoolean(false);
    else if (left.isEmpty() || right.isEmpty())
      return new ArrayList<Base>();
    else if (convertToBoolean(left) && convertToBoolean(right))
      return makeBoolean(true);
    else
      return makeBoolean(false);
  }

  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) {
    if (left.isEmpty() && right.isEmpty())
      return new ArrayList<Base>();
    else if (convertToBoolean(left) || convertToBoolean(right))
      return makeBoolean(true);
    else if (left.isEmpty() || right.isEmpty())
      return new ArrayList<Base>();
    else
      return makeBoolean(false);
  }

  private List<Base> opXor(List<Base> left, List<Base> right) {
    if (left.isEmpty() || right.isEmpty())
      return new ArrayList<Base>();
    else
      return makeBoolean(convertToBoolean(left) ^ convertToBoolean(right));
  }

  private List<Base> opImplies(List<Base> left, List<Base> right) {
    if (!convertToBoolean(left))
      return makeBoolean(true);
    else if (right.size() == 0)
      return new ArrayList<Base>();
    else
      return makeBoolean(convertToBoolean(right));
  }


  private List<Base> opMinus(List<Base> left, List<Base> right) throws PathEngineException {
    if (left.size() == 0)
      throw new PathEngineException("Error performing -: left operand has no value");
    if (left.size() > 1)
      throw new PathEngineException("Error performing -: left operand has more than one value");
    if (!left.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing -: left operand has the wrong type (%s)", left.get(0).fhirType()));
    if (right.size() == 0)
      throw new PathEngineException("Error performing -: right operand has no value");
    if (right.size() > 1)
      throw new PathEngineException("Error performing -: right operand has more than one value");
    if (!right.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing -: right operand has the wrong type (%s)", 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
      throw new PathEngineException(String.format("Error performing -: left and right operand have incompatible or illegal types (%s, %s)", left.get(0).fhirType(), right.get(0).fhirType()));
    return result;
  }

  private List<Base> opDivideBy(List<Base> left, List<Base> right) throws PathEngineException {
    if (left.size() == 0)
      throw new PathEngineException("Error performing /: left operand has no value");
    if (left.size() > 1)
      throw new PathEngineException("Error performing /: left operand has more than one value");
    if (!left.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing -: left operand has the wrong type (%s)", left.get(0).fhirType()));
    if (right.size() == 0)
      throw new PathEngineException("Error performing /: right operand has no value");
    if (right.size() > 1)
      throw new PathEngineException("Error performing /: right operand has more than one value");
    if (!right.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing /: right operand has the wrong type (%s)", 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) {
        throw new PathEngineException(e);
      }
    }
    else
      throw new PathEngineException(String.format("Error performing /: left and right operand have incompatible or illegal types (%s, %s)", left.get(0).fhirType(), right.get(0).fhirType()));
    return result;
  }

  private List<Base> opDiv(List<Base> left, List<Base> right) throws PathEngineException {
    if (left.size() == 0)
      throw new PathEngineException("Error performing div: left operand has no value");
    if (left.size() > 1)
      throw new PathEngineException("Error performing div: left operand has more than one value");
    if (!left.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing div: left operand has the wrong type (%s)", left.get(0).fhirType()));
    if (right.size() == 0)
      throw new PathEngineException("Error performing div: right operand has no value");
    if (right.size() > 1)
      throw new PathEngineException("Error performing div: right operand has more than one value");
    if (!right.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing div: right operand has the wrong type (%s)", 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")) {
      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) {
        throw new PathEngineException(e);
      }
    }
    else
      throw new PathEngineException(String.format("Error performing div: left and right operand have incompatible or illegal types (%s, %s)", left.get(0).fhirType(), right.get(0).fhirType()));
    return result;
  }

  private List<Base> opMod(List<Base> left, List<Base> right) throws PathEngineException {
    if (left.size() == 0)
      throw new PathEngineException("Error performing mod: left operand has no value");
    if (left.size() > 1)
      throw new PathEngineException("Error performing mod: left operand has more than one value");
    if (!left.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing mod: left operand has the wrong type (%s)", left.get(0).fhirType()));
    if (right.size() == 0)
      throw new PathEngineException("Error performing mod: right operand has no value");
    if (right.size() > 1)
      throw new PathEngineException("Error performing mod: right operand has more than one value");
    if (!right.get(0).isPrimitive())
      throw new PathEngineException(String.format("Error performing mod: right operand has the wrong type (%s)", 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")) {
      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 new PathEngineException(String.format("Error performing mod: left and right operand have incompatible or illegal types (%s, %s)", left.get(0).fhirType(), right.get(0).fhirType()));
    return result;
  }


  private TypeDetails readConstantType(ExecutionTypeContext context, String constant) throws PathEngineException {
    if (constant.equals("true"))
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    else if (constant.equals("false"))
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    else if (Utilities.isInteger(constant))
      return new TypeDetails(CollectionStatus.SINGLETON, "integer");
    else if (Utilities.isDecimal(constant, false))
      return new TypeDetails(CollectionStatus.SINGLETON, "decimal");
    else if (constant.startsWith("%"))
      return resolveConstantType(context, constant);
    else
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
  }

  private TypeDetails resolveConstantType(ExecutionTypeContext context, String s) throws PathEngineException {
    if (s.equals("%sct"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (s.equals("%loinc"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (s.equals("%ucum"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (s.equals("%resource")) {
      if (context.getResource() == null)
        throw new PathEngineException("%resource cannot be used in this context");
      return new TypeDetails(CollectionStatus.SINGLETON, context.getResource());
    } else if (s.equals("%context")) {
      return new TypeDetails(CollectionStatus.SINGLETON, context.getContext());
    } else if (s.equals("%map-codes"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (s.equals("%us-zip"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (s.startsWith("%\"vs-"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (s.startsWith("%\"cs-"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (s.startsWith("%\"ext-"))
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    else if (hostServices == null)
      throw new PathEngineException("Unknown fixed constant type for '"+s+"'");
    else
      return hostServices.resolveConstantType(context.getAppInfo(), s);
  }

        private List<Base> execute(ExecutionContext context, Base item, ExpressionNode exp, boolean atEntry) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    if (atEntry && Character.isUpperCase(exp.getName().charAt(0))) {// special case for start up
      if (item.isResource() && item.fhirType().equals(exp.getName()))
        result.add(item);
    } else
      getChildrenByName(item, exp.getName(), result);
    if (result.size() == 0 && atEntry && context.getAppInfo() != null) {
      Base temp = hostServices.resolveConstant(context.getAppInfo(), exp.getName());
      if (temp != null) {
        result.add(temp);
      }
    }
    return result;
  }

  private TypeDetails executeContextType(ExecutionTypeContext context, String name) throws PathEngineException, DefinitionException {
    if (hostServices == null)
      throw new PathEngineException("Unable to resolve context reference since no host services are provided");
    return hostServices.resolveConstantType(context.getAppInfo(), name);
  }

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


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


  @SuppressWarnings("unchecked")
  private TypeDetails evaluateFunctionType(ExecutionTypeContext context, TypeDetails focus, ExpressionNode exp) throws PathEngineException, DefinitionException {
    List<TypeDetails> paramTypes = new ArrayList<TypeDetails>();
    if (exp.getFunction() == Function.Is || exp.getFunction() == Function.As)
      paramTypes.add(new TypeDetails(CollectionStatus.SINGLETON, "string"));
    else
      for (ExpressionNode expr : exp.getParameters()) {
        if (exp.getFunction() == Function.Where || exp.getFunction() == Function.Select || exp.getFunction() == Function.Repeat)
          paramTypes.add(executeType(changeThis(context, focus), focus, expr, true));
        else
          paramTypes.add(executeType(context, focus, expr, true));
      }
    switch (exp.getFunction()) {
    case Empty :
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Not :
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Exists :
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case SubsetOf : {
      checkParamTypes(exp.getFunction().toCode(), paramTypes, focus);
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case SupersetOf : {
      checkParamTypes(exp.getFunction().toCode(), paramTypes, focus);
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case IsDistinct :
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Distinct :
      return focus;
    case Count :
      return new TypeDetails(CollectionStatus.SINGLETON, "integer");
    case Where :
      return focus;
    case Select :
      return anything(focus.getCollectionStatus());
    case All :
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Repeat :
      return anything(focus.getCollectionStatus());
    case Item : {
      checkOrdered(focus, "item");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "integer"));
      return focus;
    }
    case As : {
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, exp.getParameters().get(0).getName());
    }
    case Is : {
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case Single :
      return focus.toSingleton();
    case First : {
      checkOrdered(focus, "first");
      return focus.toSingleton();
    }
    case Last : {
      checkOrdered(focus, "last");
      return focus.toSingleton();
    }
    case Tail : {
      checkOrdered(focus, "tail");
      return focus;
    }
    case Skip : {
      checkOrdered(focus, "skip");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "integer"));
      return focus;
    }
    case Take : {
      checkOrdered(focus, "take");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "integer"));
      return focus;
    }
    case Iif : {
      TypeDetails types = new TypeDetails(null);
      types.update(paramTypes.get(0));
      if (paramTypes.size() > 1)
        types.update(paramTypes.get(1));
      return types;
    }
    case ToInteger : {
      checkContextPrimitive(focus, "toInteger");
      return new TypeDetails(CollectionStatus.SINGLETON, "integer");
    }
    case ToDecimal : {
      checkContextPrimitive(focus, "toDecimal");
      return new TypeDetails(CollectionStatus.SINGLETON, "decimal");
    }
    case ToString : {
      checkContextPrimitive(focus, "toString");
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    }
    case Substring : {
      checkContextString(focus, "subString");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "integer"), new TypeDetails(CollectionStatus.SINGLETON, "integer"));
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    }
    case StartsWith : {
      checkContextString(focus, "startsWith");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case EndsWith : {
      checkContextString(focus, "endsWith");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case Matches : {
      checkContextString(focus, "matches");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case ReplaceMatches : {
      checkContextString(focus, "replaceMatches");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"), new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    }
    case Contains : {
      checkContextString(focus, "contains");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case Replace : {
      checkContextString(focus, "replace");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"), new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "string");
    }
    case Length : {
      checkContextPrimitive(focus, "length");
      return new TypeDetails(CollectionStatus.SINGLETON, "integer");
    }
    case Children :
      return childTypes(focus, "*");
    case Descendants :
      return childTypes(focus, "**");
    case MemberOf : {
      checkContextCoded(focus, "memberOf");
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    }
    case Trace : {
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return focus;
    }
    case Today :
      return new TypeDetails(CollectionStatus.SINGLETON, "date");
    case Now :
      return new TypeDetails(CollectionStatus.SINGLETON, "dateTime");
    case Resolve : {
      checkContextReference(focus, "resolve");
      return new TypeDetails(CollectionStatus.SINGLETON, "DomainResource");
    }
    case Extension : {
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return new TypeDetails(CollectionStatus.SINGLETON, "Extension");
    }
    case HasValue :
      return new TypeDetails(CollectionStatus.SINGLETON, "boolean");
    case Alias :
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return anything(CollectionStatus.SINGLETON);
    case AliasAs :
      checkParamTypes(exp.getFunction().toCode(), paramTypes, new TypeDetails(CollectionStatus.SINGLETON, "string"));
      return focus;
    case Custom : {
      return hostServices.checkFunction(context.getAppInfo(), exp.getName(), paramTypes);
    }
    default:
      break;
    }
    throw new Error("not Implemented yet");
  }


  private void checkParamTypes(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 new PathEngineException("The parameter type '"+a+"' is not legal for "+funcName+" parameter "+Integer.toString(i)+". expecting "+pt.toString());
      }
    }
  }

  private void checkOrdered(TypeDetails focus, String name) throws PathEngineException {
    if (focus.getCollectionStatus() == CollectionStatus.UNORDERED)
      throw new PathEngineException("The function '"+name+"'() can only be used on ordered collections");
  }

  private void checkContextReference(TypeDetails focus, String name) throws PathEngineException {
    if (!focus.hasType(worker, "string") && !focus.hasType(worker, "uri") && !focus.hasType(worker, "Reference"))
      throw new PathEngineException("The function '"+name+"'() can only be used on string, uri, Reference");
  }


  private void checkContextCoded(TypeDetails focus, String name) throws PathEngineException {
    if (!focus.hasType(worker, "string") && !focus.hasType(worker, "code") && !focus.hasType(worker, "uri") && !focus.hasType(worker, "Coding") && !focus.hasType(worker, "CodeableConcept"))
      throw new PathEngineException("The function '"+name+"'() can only be used on string, code, uri, Coding, CodeableConcept");
  }


  private void checkContextString(TypeDetails focus, String name) throws PathEngineException {
    if (!focus.hasType(worker, "string") && !focus.hasType(worker, "code") && !focus.hasType(worker, "uri") && !focus.hasType(worker, "id"))
      throw new PathEngineException("The function '"+name+"'() can only be used on string, uri, code, id, but found "+focus.describe());
  }


  private void checkContextPrimitive(TypeDetails focus, String name) throws PathEngineException {
    if (!focus.hasType(primitiveTypes))
      throw new PathEngineException("The function '"+name+"'() can only be used on "+primitiveTypes.toString());
  }


  private TypeDetails childTypes(TypeDetails focus, String mask) throws PathEngineException, DefinitionException {
    TypeDetails result = new TypeDetails(CollectionStatus.UNORDERED);
    for (String f : focus.getTypes())
      getChildTypesByName(f, mask, result);
    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 Item : return funcItem(context, focus, exp);
    case As : return funcAs(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 Iif : return funcIif(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 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 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 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 HasValue : return funcHasValue(context, focus, exp);
    case AliasAs : return funcAliasAs(context, focus, exp);
    case Alias : return funcAlias(context, focus, exp);
    case Custom: {
      List<List<Base>> params = new ArrayList<List<Base>>();
      for (ExpressionNode p : exp.getParameters())
        params.add(execute(context, focus, p, true));
      return hostServices.executeFunction(context.getAppInfo(), exp.getName(), params);
    }
    default:
      throw new Error("not Implemented yet");
    }
  }

        private List<Base> funcAliasAs(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();
    context.addAlias(name, focus);
    return focus;
  }

  private List<Base> funcAlias(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> res = new ArrayList<Base>();
    Base b = context.getAlias(name);
    if (b != null)
      res.add(b);
    return res;

  }

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


  private ExecutionContext changeThis(ExecutionContext context, Base newThis) {
    return new ExecutionContext(context.getAppInfo(), context.getResource(), context.getContext(), context.getAliases(), newThis);
  }

  private ExecutionTypeContext changeThis(ExecutionTypeContext context, TypeDetails newThis) {
    return new ExecutionTypeContext(context.getAppInfo(), context.getResource(), context.getContext(), newThis);
  }


  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) {
    throw new Error("not Implemented yet");
  }


  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 exp) throws FHIRException, PathEngineException {
    List<Base> result = new ArrayList<Base>();

    if (focus.size() == 1) {
      String f = convertToString(focus.get(0));

      if (!Utilities.noString(f)) {

        if (exp.getParameters().size() == 2) {

          String t = convertToString(execute(context, focus, exp.getParameters().get(0), true));
          String r = convertToString(execute(context, focus, exp.getParameters().get(1), true));

          String n = f.replace(t, r);
          result.add(new StringType(n));
        }
        else {
          throw new PathEngineException(String.format("funcReplace() : checking for 2 arguments (pattern, substitution) but found %d items", exp.getParameters().size()));
        }
      }
      else {
        throw new PathEngineException(String.format("funcReplace() : checking for 1 string item but found empty item"));
      }
    }
    else {
      throw new PathEngineException(String.format("funcReplace() : checking for 1 string item but found %d items", focus.size()));
    }
    return result;
  }


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

    if (focus.size() == 1 && !Utilities.noString(regex)) {
      result.add(new StringType(convertToString(focus.get(0)).replaceAll(regex, repl)));
    } else {
      result.add(new StringType(convertToString(focus.get(0))));
    }
    return result;
  }


  private List<Base> funcEndsWith(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))
      result.add(new BooleanType(convertToString(focus.get(0)).endsWith(sw)));
    else
      result.add(new BooleanType(false));
    return result;
  }


  private List<Base> funcToString(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    result.add(new StringType(convertToString(focus)));
    return result;
  }


  private List<Base> funcToDecimal(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    String s = convertToString(focus);
    List<Base> result = new ArrayList<Base>();
    if (Utilities.isDecimal(s, true))
      result.add(new DecimalType(s));
    return result;
  }


  private List<Base> funcIif(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> n1 = execute(context, focus, exp.getParameters().get(0), true);
    Boolean v = convertToBoolean(n1);

    if (v)
      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> funcSingle(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws PathEngineException {
    if (focus.size() == 1)
      return focus;
    throw new PathEngineException(String.format("Single() : checking for 1 item but found %d items", focus.size()));
  }


  private List<Base> funcIs(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws PathEngineException {
    List<Base> result = new ArrayList<Base>();
    if (focus.size() == 0 || focus.size() > 1)
      result.add(new BooleanType(false));
    else {
      String tn = exp.getParameters().get(0).getName();
      result.add(new BooleanType(focus.get(0).hasType(tn)));
    }
    return result;
  }


  private List<Base> funcAs(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    String tn = exp.getParameters().get(0).getName();
    for (Base b : focus)
      if (b.hasType(tn))
        result.add(b);
    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 = !added.isEmpty();
      result.addAll(added);
      current.clear();
      current.addAll(added);
    }
    return result;
  }



  private List<Base> funcIsDistinct(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    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++) {
        if (doEquals(focus.get(j), focus.get(i))) {
          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));
    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));
    return result;
  }


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


  private List<Base> funcResolve(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    List<Base> result = new ArrayList<Base>();
    for (Base item : focus) {
        String s = convertToString(item);
        if (item.fhirType().equals("Reference")) {
          Property p = item.getChildByName("reference");
        if (p.hasValues())
            s = convertToString(p.getValues().get(0));
        }
        Base res = null;
        if (s.startsWith("#")) {
          Property p = context.getResource().getChildByName("contained");
          for (Base c : p.getValues()) {
          if (s.equals(c.getIdBase()))
              res = c;
        }
      } else if (hostServices != null) {
         res = hostServices.resolveReference(context.getAppInfo(), s);
      }
        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> 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();

    log(name, focus);
    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++) {
        if (doEquals(focus.get(j), focus.get(i))) {
          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>();
    String sw = convertToString(execute(context, focus, exp.getParameters().get(0), true));

    if (focus.size() == 1 && !Utilities.noString(sw)) {
      String st = convertToString(focus.get(0));
      if (Utilities.noString(st))
        result.add(new BooleanType(false));
      else
        result.add(new BooleanType(st.matches(sw)));
    } else
      result.add(new BooleanType(false));
    return result;
  }

        private List<Base> funcContains(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)) {
      String st = convertToString(focus.get(0));
      if (Utilities.noString(st))
        result.add(new BooleanType(false));
      else
        result.add(new BooleanType(st.contains(sw)));
    }  else
      result.add(new BooleanType(false));
    return result;
  }

  private List<Base> funcLength(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 IntegerType(s.length()));
    }
    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)));
    }
    return result;
  }

        private List<Base> funcStartsWith(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))
      result.add(new BooleanType(convertToString(focus.get(0)).startsWith(sw)));
    else
      result.add(new BooleanType(false));
    return result;
  }

        private List<Base> funcSubstring(ExecutionContext context, List<Base> focus, ExpressionNode exp) throws FHIRException {
    List<Base> result = new ArrayList<Base>();
    List<Base> n1 = execute(context, focus, exp.getParameters().get(0), true);
    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);
      i2 = Integer.parseInt(n2.get(0).primitiveValue());
    }

    if (focus.size() == 1) {
      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));
    }
    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));
    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()));
    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 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);
      if (convertToBoolean(execute(changeThis(context, item), pc, exp.getParameters().get(0), 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>();
    for (Base item : focus) {
      pc.clear();
      pc.add(item);
      result.addAll(execute(changeThis(context, item), pc, exp.getParameters().get(0), true));
    }
    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)));
    return result;
  }

  private List<Base> funcNot(ExecutionContext context, List<Base> focus, ExpressionNode exp) {
    return makeBoolean(!convertToBoolean(focus));
  }

  private class ElementDefinitionMatch {
    private ElementDefinition definition;
    private String fixedType;
    public ElementDefinitionMatch(ElementDefinition definition, String fixedType) {
      super();
      this.definition = definition;
      this.fixedType = fixedType;
    }
    public ElementDefinition getDefinition() {
      return definition;
    }
    public String getFixedType() {
      return fixedType;
    }

  }

  private void getChildTypesByName(String type, String name, TypeDetails result) throws PathEngineException, DefinitionException {
    if (Utilities.noString(type))
      throw new PathEngineException("No type provided in BuildToolPathEvaluator.getChildTypesByName");
    if (type.equals("http://hl7.org/fhir/StructureDefinition/xhtml"))
      return;
    String url = null;
    if (type.contains("#")) {
      url = type.substring(0, type.indexOf("#"));
    } else {
      url = type;
    }
    String tail = "";
    StructureDefinition sd = worker.fetchResource(StructureDefinition.class, url);
    if (sd == null)
      throw new DefinitionException("Unknown type "+type); // this really is an error, because we can only get to here if the internal infrastrucgture is wrong
    List<StructureDefinition> sdl = new ArrayList<StructureDefinition>();
    ElementDefinitionMatch m = null;
    if (type.contains("#"))
      m = getElementDefinition(sd, type.substring(type.indexOf("#")+1), false);
    if (m != null && hasDataType(m.definition)) {
      if (m.fixedType != null)
      {
        StructureDefinition dt = worker.fetchTypeDefinition(m.fixedType);
        if (dt == null)
          throw new DefinitionException("unknown data type "+m.fixedType);
        sdl.add(dt);
      } else
        for (TypeRefComponent t : m.definition.getType()) {
          StructureDefinition dt = worker.fetchTypeDefinition(t.getCode());
          if (dt == null)
            throw new DefinitionException("unknown data type "+t.getCode());
          sdl.add(dt);
        }
    } else {
      sdl.add(sd);
      if (type.contains("#")) {
        tail = type.substring(type.indexOf("#")+1);
        tail = tail.substring(tail.indexOf("."));
      }
    }

    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))
            for (TypeRefComponent t : ed.getType()) {
              if (t.hasCode() && t.getCodeElement().hasValue()) {
                String tn = null;
                if (t.getCode().equals("Element") || t.getCode().equals("BackboneElement"))
                  tn = sdi.getType()+"#"+ed.getPath();
                else
                  tn = t.getCode();
                if (t.getCode().equals("Resource")) {
                  for (String rn : worker.getResourceNames()) {
                    if (!result.hasType(worker, rn)) {
                      getChildTypesByName(result.addType(rn), "**", result);
                    }
                  }
                } else if (!result.hasType(worker, tn)) {
                  getChildTypesByName(result.addType(tn), "**", result);
                }
              }
            }
        }
      } 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 (t.getCode().equals("Element") || t.getCode().equals("BackboneElement"))
                result.addType(sdi.getType()+"#"+ed.getPath());
              else if (t.getCode().equals("Resource"))
                result.addTypes(worker.getResourceNames());
              else
                result.addType(t.getCode());
            }
        }
      } else {
        path = sdi.getSnapshot().getElement().get(0).getPath()+tail+"."+name;

        ElementDefinitionMatch ed = getElementDefinition(sdi, path, false);
        if (ed != null) {
          if (!Utilities.noString(ed.getFixedType()))
            result.addType(ed.getFixedType());
          else
            for (TypeRefComponent t : ed.getDefinition().getType()) {
              if (Utilities.noString(t.getCode()))
                break; // throw new PathEngineException("Illegal reference to primitive value attribute @ "+path);

              ProfiledType pt = null;
              if (t.getCode().equals("Element") || t.getCode().equals("BackboneElement"))
                pt = new ProfiledType(sdi.getUrl()+"#"+path);
              else if (t.getCode().equals("Resource"))
                result.addTypes(worker.getResourceNames());
              else
                pt = new ProfiledType(t.getCode());
              if (pt != null) {
                if (t.hasProfile())
                  pt.addProfile(t.getProfile());
                if (ed.getDefinition().hasBinding())
                  pt.addBinding(ed.getDefinition().getBinding());
                result.addType(pt);
              }
            }
        }
      }
    }
  }

  private ElementDefinitionMatch getElementDefinition(StructureDefinition sd, String path, boolean allowTypedName) throws PathEngineException {
    for (ElementDefinition ed : sd.getSnapshot().getElement()) {
      if (ed.getPath().equals(path)) {
        if (ed.hasContentReference()) {
          return getElementDefinitionById(sd, ed.getContentReference());
        } else
          return 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 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 new ElementDefinitionMatch(ed, s);
        else
        return 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
          throw new PathEngineException("Internal typing issue....");
        StructureDefinition nsd = worker.fetchTypeDefinition(ed.getType().get(0).getCode());
            if (nsd == null)
              throw new PathEngineException("Unknown type "+ed.getType().get(0).getCode());
        return getElementDefinition(nsd, nsd.getId()+path.substring(ed.getPath().length()), allowTypedName);
      }
      if (ed.hasContentReference() && path.startsWith(ed.getPath()+".")) {
        ElementDefinitionMatch m = getElementDefinitionById(sd, ed.getContentReference());
        return getElementDefinition(sd, m.definition.getPath()+path.substring(ed.getPath().length()), allowTypedName);
      }
    }
    return null;
  }

  private boolean isAbstractType(List<TypeRefComponent> list) {
        return list.size() != 1 ? true : Utilities.existsInList(list.get(0).getCode(), "Element", "BackboneElement", "Resource", "DomainResource");
}


  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"));
  }

  private ElementDefinitionMatch getElementDefinitionById(StructureDefinition sd, String ref) {
    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;
  }

}