net.sf.saxon.expr
Class LetExpression

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.Assignation
          net.sf.saxon.expr.LetExpression

All Implemented Interfaces:

Serializable, Binding, Expression

public class LetExpression
extends Assignation

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

Field Summary

Fields inherited from class net.sf.saxon.expr.Assignation

action, declaration, sequence, slotNumber, variableName

Fields inherited from class net.sf.saxon.expr.ComputedExpression

lineNumber, NO_ARGUMENTS, staticProperties

Constructor Summary

LetExpression()

Method Summary

Expression	analyze(StaticContext env) Type-check the expression
int	computeCardinality() Determine the static cardinality of the expression
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
void	display(int level, NamePool pool) Diagnostic print of expression structure
Item	evaluateItem(XPathContext context) Evaluate the expression as a singleton
ItemType	getItemType() Determine the data type of the items returned by the expression, if possible
SequenceType	getRequiredType() Get data type of the range variable (part of the Binding interface)
SequenceIterator	iterate(XPathContext context) Iterate over the sequence of values
boolean	markTailFunctionCalls() Mark tail function calls
Expression	promote(PromotionOffer offer) Promote this expression if possible

Methods inherited from class net.sf.saxon.expr.Assignation

evaluateVariable, getSubExpressions, getVariableName, setAction, setSequence, setSlotNumber, setVariableDeclaration, simplify

Methods inherited from class net.sf.saxon.expr.ComputedExpression

computeDependencies, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getDependencies, getIntrinsicDependencies, getLineNumber, getSpecialProperties, setLineNumber, typeError

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LetExpression

public LetExpression()

Method Detail

analyze

public Expression analyze(StaticContext env)
                   throws XPathException

Type-check the expression

Parameters:

env - the static context of the expression

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)

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the sequence of values

Specified by:

iterate in interface Expression

Overrides:

iterate in class ComputedExpression

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

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the expression as a singleton

Specified by:

evaluateItem in interface Expression

Overrides:

evaluateItem in class ComputedExpression

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

getItemType

public ItemType getItemType()

Determine the data type of the items returned by the expression, if possible

Returns:

one of the values Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)

getRequiredType

public SequenceType getRequiredType()

Get data type of the range variable (part of the Binding interface)

Specified by:

getRequiredType in interface Binding

Overrides:

getRequiredType in class Assignation

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Specified by:

computeCardinality in class ComputedExpression

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 class ComputedExpression

markTailFunctionCalls

public boolean markTailFunctionCalls()

Mark tail function calls

Overrides:

markTailFunctionCalls in class ComputedExpression

Returns:

true if a tail recursive call was found and if this call accounts for the whole of the value.

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

Specified by:

promote in interface Expression

Overrides:

promote in class Assignation

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

display

public void display(int level,
                    NamePool pool)

Diagnostic print of expression structure

Parameters:

level - indentation level for this expression