Package net.sf.saxon.expr
Class LetExpression
- java.lang.Object
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- net.sf.saxon.expr.Expression
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- net.sf.saxon.expr.Assignation
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- net.sf.saxon.expr.LetExpression
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- All Implemented Interfaces:
Binding,ExportAgent,TailCallReturner,LocalBinding,Locatable,IdentityComparable,Traceable
- Direct Known Subclasses:
EagerLetExpression
public class LetExpression extends Assignation implements TailCallReturner
A LetExpression represents the XQuery construct let $x := expr return expr. It is used also for XSLT local variables.
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Field Summary
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Fields inherited from class net.sf.saxon.expr.Assignation
hasLoopingReference, isIndexedVariable, references, requiredType, slotNumber, variableName
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Fields inherited from class net.sf.saxon.expr.Expression
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD
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Constructor Summary
Constructors Constructor Description LetExpression()Create a LetExpression
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description voidcheckPermittedContents(SchemaType parentType, boolean whole)Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.intcomputeCardinality()Determine the static cardinality of the expressionintcomputeSpecialProperties()Get the static properties of this expression (other than its type).Expressioncopy(RebindingMap rebindings)Copy an expression.booleaneffectiveBooleanValue(XPathContext context)Get the effective boolean value of the expression.Sequenceeval(XPathContext context)Evaluate the variable.ItemevaluateItem(XPathContext context)Evaluate the expression as a singletonvoidevaluatePendingUpdates(XPathContext context, PendingUpdateList pul)Evaluate an updating expression, adding the results to a Pending Update List.voidexport(ExpressionPresenter out)Diagnostic print of expression structure.voidgatherProperties(java.util.function.BiConsumer<java.lang.String,java.lang.Object> consumer)Get the properties of this object to be included in trace messages, by supplying the property values to a supplied consumer functiondoublegetCost()Return the estimated cost of evaluating an expression.EvaluatorgetEvaluator()java.lang.StringgetExpressionName()Get a name identifying the kind of expression, in terms meaningful to a user.intgetImplementationMethod()An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().IntegerValue[]getIntegerBounds()For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.ItemTypegetItemType()Determine the data type of the items returned by the expression, if possibleUTypegetStaticUType(UType contextItemType)Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.booleanimplementsStaticTypeCheck()Determine whether this expression implements its own method for static type checkingbooleanisInstruction()Ask whether this expression is an instruction.booleanisLiftable(boolean forStreaming)Ask whether the expression can be lifted out of a loop, assuming it has no dependencies on the controlling variable/focus of the loopbooleanisNeedsLazyEvaluation()booleanisVacuousExpression()Determine whether this is a vacuous expression as defined in the XQuery update specificationSequenceIteratoriterate(XPathContext context)Iterate over the result of the expression to return a sequence of itemsintmarkTailFunctionCalls(StructuredQName qName, int arity)Mark tail function callsExpressionoptimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType)Perform optimisation of an expression and its subexpressions.voidprocess(Outputter output, XPathContext context)Process this expression as an instruction, writing results to the current outputterTailCallprocessLeavingTail(Outputter output, XPathContext context)ProcessLeavingTail: called to do the real work of this instruction.voidresetLocalStaticProperties()Reset the static properties of the expression to -1, so that they have to be recomputed next time they are used.voidsetEvaluationMode(EvaluationMode mode)voidsetEvaluator()voidsetEvaluator(Evaluator evaluator)voidsetInstruction(boolean inst)Say whether this expression originates as an XSLT instructionvoidsetNeedsEagerEvaluation(boolean req)Say that this variable must be evaluated eagerly.voidsetNeedsLazyEvaluation(boolean req)ExpressionstaticTypeCheck(SequenceType req, boolean backwardsCompatible, RoleDiagnostic role, ExpressionVisitor visitor)Static type checking for let expressions is delegated to the expression itself, and is performed on the "action" expression, to allow further delegation to the branches of a conditionaljava.lang.StringtoShortString()Produce a short string identifying the expression for use in error messagesjava.lang.StringtoString()The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.ExpressiontypeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)Type-check the expression.-
Methods inherited from class net.sf.saxon.expr.Assignation
addReference, addToPathMap, checkForUpdatingSubexpressions, computeDependencies, evaluateVariable, getAction, getActionOp, getIntegerBoundsForVariable, getLocalSlotNumber, getNominalReferenceCount, getObjectName, getRequiredSlots, getRequiredType, getSequence, getSequenceOp, getVariableEQName, getVariableName, getVariableQName, hasVariableBinding, isAssignable, isGlobal, isIndexedVariable, isUpdatingExpression, operands, rebuildReferenceList, refineTypeInformation, removeDeadReferences, replaceVariable, setAction, setIndexedVariable, setRequiredType, setSequence, setSlotNumber, setVariableQName, suppressValidation, unordered, verifyReferences
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Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, computeHashCode, computeStaticProperties, dynamicError, equals, evaluateAsString, explain, getCardinality, getConfiguration, getDependencies, getEvaluationMethod, getExtraProperty, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStreamerName, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, identityHashCode, isCallOn, isEqual, isIdentical, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, operandList, operandSparseList, optimizeChildren, prepareForStreaming, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, toPattern, typeCheckChildren, typeError, verifyParentPointers
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Method Detail
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setInstruction
public void setInstruction(boolean inst)
Say whether this expression originates as an XSLT instruction- Parameters:
inst- true if this is an xsl:variable instruction
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isInstruction
public boolean isInstruction()
Ask whether this expression is an instruction. In XSLT streamability analysis this is used to distinguish constructs corresponding to XSLT instructions from other constructs.- Overrides:
isInstructionin classExpression- Returns:
- true if this construct originates as an XSLT instruction
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getExpressionName
public java.lang.String getExpressionName()
Get a name identifying the kind of expression, in terms meaningful to a user.- Overrides:
getExpressionNamein classExpression- Returns:
- a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.
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setNeedsEagerEvaluation
public void setNeedsEagerEvaluation(boolean req)
Say that this variable must be evaluated eagerly. This is a requirement for example for variables appearing within a try/catch, or for variables referenced from within a construct that uses multi-threading, for example xsl:result-document or a multi-threaded xsl:for-each.- Parameters:
req- set to true if eager evaluation is required
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setNeedsLazyEvaluation
public void setNeedsLazyEvaluation(boolean req)
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isNeedsLazyEvaluation
public boolean isNeedsLazyEvaluation()
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isLiftable
public boolean isLiftable(boolean forStreaming)
Ask whether the expression can be lifted out of a loop, assuming it has no dependencies on the controlling variable/focus of the loop- Overrides:
isLiftablein classExpression- Parameters:
forStreaming- true if we are handling streaming code (where rewrites need to be more cautious)- Returns:
- true if the expression can be loop lifted
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resetLocalStaticProperties
public void resetLocalStaticProperties()
Description copied from class:ExpressionReset the static properties of the expression to -1, so that they have to be recomputed next time they are used.- Overrides:
resetLocalStaticPropertiesin classExpression
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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
Type-check the expression. This also has the side-effect of counting the number of references to the variable (treating references that occur within a loop specially)- Overrides:
typeCheckin classExpression- Parameters:
visitor- an expression visitorcontextInfo- Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.- Returns:
- the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
- Throws:
XPathException- if an error is discovered during this phase (typically a type error)
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implementsStaticTypeCheck
public boolean implementsStaticTypeCheck()
Determine whether this expression implements its own method for static type checking- Overrides:
implementsStaticTypeCheckin classExpression- Returns:
- true - this expression has a non-trivial implementation of the staticTypeCheck() method
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staticTypeCheck
public Expression staticTypeCheck(SequenceType req, boolean backwardsCompatible, RoleDiagnostic role, ExpressionVisitor visitor) throws XPathException
Static type checking for let expressions is delegated to the expression itself, and is performed on the "action" expression, to allow further delegation to the branches of a conditional- Overrides:
staticTypeCheckin classExpression- Parameters:
req- the required typebackwardsCompatible- true if backwards compatibility mode appliesrole- the role of the expression in relation to the required typevisitor- an expression visitor- Returns:
- the expression after type checking (perhaps augmented with dynamic type checking code)
- Throws:
XPathException- if failures occur, for example if the static type of one branch of the conditional is incompatible with the required type
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optimize
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException
Perform optimisation of an expression and its subexpressions.This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.
- Overrides:
optimizein classExpression- Parameters:
visitor- an expression visitorcontextItemType- the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set toType.ITEM_TYPE- Returns:
- the original expression, rewritten if appropriate to optimize execution
- Throws:
XPathException- if an error is discovered during this phase (typically a type error)
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setEvaluator
public void setEvaluator()
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getCost
public double getCost()
Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.- Overrides:
getCostin classAssignation- Returns:
- a rough estimate of the evaluation cost
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isVacuousExpression
public boolean isVacuousExpression()
Determine whether this is a vacuous expression as defined in the XQuery update specification- Overrides:
isVacuousExpressionin classExpression- Returns:
- true if this expression is vacuous
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checkPermittedContents
public void checkPermittedContents(SchemaType parentType, boolean whole) throws XPathException
Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.- Overrides:
checkPermittedContentsin classExpression- Parameters:
parentType- the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this typewhole- if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content- Throws:
XPathException- if the value delivered by this expression cannot be part of the content model of the given type
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getIntegerBounds
public IntegerValue[] getIntegerBounds()
For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.- Overrides:
getIntegerBoundsin classExpression- Returns:
- the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.
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getImplementationMethod
public int getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.- Specified by:
getImplementationMethodin classExpression- Returns:
- the implementation method, for example
Expression.ITERATE_METHODorExpression.EVALUATE_METHODorExpression.PROCESS_METHOD
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gatherProperties
public void gatherProperties(java.util.function.BiConsumer<java.lang.String,java.lang.Object> consumer)
Get the properties of this object to be included in trace messages, by supplying the property values to a supplied consumer function- Specified by:
gatherPropertiesin interfaceTraceable- Parameters:
consumer- the function to which the properties should be supplied, as (property name, value) pairs.
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Iterate over the result of the expression to return a sequence of items- Overrides:
iteratein classExpression- Parameters:
context- supplies the context for evaluation- Returns:
- a SequenceIterator that can be used to iterate over the result of the expression
- Throws:
XPathException- if any dynamic error occurs evaluating the expression
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eval
public Sequence eval(XPathContext context) throws XPathException
Evaluate the variable.- Parameters:
context- the dynamic evaluation context- Returns:
- the result of evaluating the expression that is bound to the variable
- Throws:
XPathException
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evaluateItem
public Item evaluateItem(XPathContext context) throws XPathException
Evaluate the expression as a singleton- Overrides:
evaluateItemin classExpression- Parameters:
context- The context in which the expression is to be evaluated- Returns:
- the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
- Throws:
XPathException- if any dynamic error occurs evaluating the expression
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effectiveBooleanValue
public boolean effectiveBooleanValue(XPathContext context) throws XPathException
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.- Overrides:
effectiveBooleanValuein classExpression- Parameters:
context- The context in which the expression is to be evaluated- Returns:
- the effective boolean value
- Throws:
XPathException- if any dynamic error occurs evaluating the expression
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process
public void process(Outputter output, XPathContext context) throws XPathException
Process this expression as an instruction, writing results to the current outputter- Overrides:
processin classExpression- Parameters:
output- the destination for the resultcontext- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException- if a dynamic error occurs
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getItemType
public ItemType getItemType()
Determine the data type of the items returned by the expression, if possible- Specified by:
getItemTypein classExpression- Returns:
- one of the values Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)
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getStaticUType
public UType getStaticUType(UType contextItemType)
Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.- Overrides:
getStaticUTypein classExpression- Parameters:
contextItemType- the type of the context item- Returns:
- the static item type of the expression according to the XSLT 3.0 defined rules
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computeCardinality
public int computeCardinality()
Determine the static cardinality of the expression- Specified by:
computeCardinalityin classExpression- Returns:
- the computed cardinality, as one of the values
StaticProperty.ALLOWS_ZERO_OR_ONE,StaticProperty.EXACTLY_ONE,StaticProperty.ALLOWS_ONE_OR_MORE,StaticProperty.ALLOWS_ZERO_OR_MORE. May also returnStaticProperty.ALLOWS_ZEROif the result is known to be an empty sequence, orStaticProperty.ALLOWS_MANYif if is known to return a sequence of length two or more.
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computeSpecialProperties
public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.- Overrides:
computeSpecialPropertiesin classExpression- Returns:
- the special properties, as a bit-significant integer
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markTailFunctionCalls
public int markTailFunctionCalls(StructuredQName qName, int arity)
Mark tail function calls- Overrides:
markTailFunctionCallsin classExpression- Parameters:
qName- the name of the functionarity- the arity (number of parameters) of the function- Returns:
UserFunctionCall.NOT_TAIL_CALLif no tail call was found;UserFunctionCall.FOREIGN_TAIL_CALLif a tail call on a different function was found;UserFunctionCall.SELF_TAIL_CALLif a tail recursive call was found and if this call accounts for the whole of the value.
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copy
public Expression copy(RebindingMap rebindings)
Copy an expression. This makes a deep copy.- Specified by:
copyin classExpression- Parameters:
rebindings- variables whose binding needs to change- Returns:
- the copy of the original expression
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processLeavingTail
public TailCall processLeavingTail(Outputter output, XPathContext context) throws XPathException
ProcessLeavingTail: called to do the real work of this instruction. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.- Specified by:
processLeavingTailin interfaceTailCallReturner- Parameters:
output- the destination for the resultcontext- The dynamic context of the transformation, giving access to the current node, the current variables, etc.- Returns:
- null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
- Throws:
XPathException- if a dynamic error occurs during the evaluation of the instruction
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evaluatePendingUpdates
public void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) throws XPathException
Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException- Overrides:
evaluatePendingUpdatesin classExpression- Parameters:
context- the XPath dynamic evaluation contextpul- the pending update list to which the results should be written- Throws:
XPathException- if evaluation fails
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toString
public java.lang.String toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax- Overrides:
toStringin classExpression- Returns:
- a representation of the expression as a string
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toShortString
public java.lang.String toShortString()
Produce a short string identifying the expression for use in error messages- Overrides:
toShortStringin classExpression- Returns:
- a short string, sufficient to identify the expression
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export
public void export(ExpressionPresenter out) throws XPathException
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
exportin interfaceExportAgent- Specified by:
exportin classExpression- Parameters:
out- the expression presenter used to display the structure- Throws:
XPathException- if the export fails, for example if an expression is found that won't work in the target environment.
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setEvaluator
public void setEvaluator(Evaluator evaluator)
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setEvaluationMode
public void setEvaluationMode(EvaluationMode mode)
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getEvaluator
public Evaluator getEvaluator()
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