Package net.sf.saxon.expr
Class LetExpression
- java.lang.Object
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- net.sf.saxon.expr.ComputedExpression
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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:
java.io.Serializable
,javax.xml.transform.SourceLocator
,Binding
,Container
,Expression
,TailCallReturner
,InstructionInfoProvider
- Direct Known Subclasses:
EagerLetExpression
public class LetExpression extends Assignation implements TailCallReturner
A LetExpression is modelled on the XQuery syntax let $x := expr return expr. This syntax is not available in the surface XPath language, but it is used internally in an optimized expression tree.- See Also:
- Serialized Form
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Field Summary
Fields Modifier and Type Field Description (package private) int
evaluationMode
(package private) int
refCount
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Fields inherited from class net.sf.saxon.expr.Assignation
action, declaration, nameCode, sequence, slotNumber, variableName
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Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
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Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
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Constructor Summary
Constructors Constructor Description LetExpression()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
checkPermittedContents(SchemaType parentType, StaticContext env, 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.int
computeCardinality()
Determine the static cardinality of the expressionint
computeSpecialProperties()
Get the static properties of this expression (other than its type).void
display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structureprotected ValueRepresentation
eval(XPathContext context)
Evaluate the variable.Item
evaluateItem(XPathContext context)
Evaluate the expression as a singletonItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possibleSequenceIterator
iterate(XPathContext context)
Iterate over the sequence of valuesboolean
markTailFunctionCalls(int nameCode, int arity)
Mark tail function callsExpression
optimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.void
process(XPathContext context)
Process this expression as an instruction, writing results to the current outputterTailCall
processLeavingTail(XPathContext context)
ProcessLeavingTail: called to do the real work of this instruction.Expression
promote(PromotionOffer offer)
Promote this expression if possiblevoid
setIndexedVariable()
Expression
typeCheck(StaticContext env, ItemType contextItemType)
Type-check the expression-
Methods inherited from class net.sf.saxon.expr.Assignation
evaluateVariable, extendBindingList, getAction, getLocalSlotNumber, getRequiredSlots, getSequence, getVariableDeclaration, getVariableFingerprint, getVariableName, getVariableNameCode, isAssignable, isGlobal, iterateSubExpressions, promoteWhereClause, replaceSubExpression, setAction, setSequence, setSlotNumber, setVariableDeclaration, simplify, suppressValidation
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Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, typeError
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Method Detail
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setIndexedVariable
public void setIndexedVariable()
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typeCheck
public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
Type-check the expression- Specified by:
typeCheck
in interfaceExpression
- Parameters:
env
- the static context of the expressioncontextItemType
- 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 to perform necessary run-time type checks, and to perform other type-related optimizations
- Throws:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
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optimize
public Expression optimize(Optimizer opt, StaticContext env, ItemType 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.
- Specified by:
optimize
in interfaceExpression
- Parameters:
opt
- the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.env
- the static context of the expressioncontextItemType
- 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:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
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checkPermittedContents
public void checkPermittedContents(SchemaType parentType, StaticContext env, 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.- Specified by:
checkPermittedContents
in interfaceExpression
- Overrides:
checkPermittedContents
in classComputedExpression
- Parameters:
parentType
- The schema typeenv
- the static contextwhole
- true if this expression is expected to make the whole content of the type, false if it is expected to make up only a part- Throws:
XPathException
- if the expression doesn't match the required content type
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Iterate over the sequence of values- Specified by:
iterate
in interfaceExpression
- Overrides:
iterate
in classComputedExpression
- 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
protected ValueRepresentation eval(XPathContext context) throws XPathException
Evaluate the variable. (This is overridden in a subclass).- Throws:
XPathException
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evaluateItem
public Item evaluateItem(XPathContext context) throws XPathException
Evaluate the expression as a singleton- Specified by:
evaluateItem
in interfaceExpression
- Overrides:
evaluateItem
in classComputedExpression
- 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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process
public void process(XPathContext context) throws XPathException
Process this expression as an instruction, writing results to the current outputter- Specified by:
process
in interfaceExpression
- Overrides:
process
in classComputedExpression
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
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getItemType
public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible- Specified by:
getItemType
in interfaceExpression
- Parameters:
th
-- 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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computeCardinality
public int computeCardinality()
Determine the static cardinality of the expression- Specified by:
computeCardinality
in classComputedExpression
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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:
computeSpecialProperties
in classComputedExpression
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markTailFunctionCalls
public boolean markTailFunctionCalls(int nameCode, int arity)
Mark tail function calls- Overrides:
markTailFunctionCalls
in classComputedExpression
- Returns:
- true if a tail recursive call was found and if this call accounts for the whole of the value.
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promote
public Expression promote(PromotionOffer offer) throws XPathException
Promote this expression if possible- Specified by:
promote
in interfaceExpression
- Overrides:
promote
in classAssignation
- Parameters:
offer
- details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression- Returns:
- if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
- Throws:
XPathException
- if any error is detected
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processLeavingTail
public TailCall processLeavingTail(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:
processLeavingTail
in interfaceTailCallReturner
- Parameters:
context
- 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
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display
public void display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structure- Specified by:
display
in interfaceExpression
- Parameters:
level
- indentation level for this expressionout
- Output destination
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