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:
Binding, Expression, Instr, Locatable, java.io.Serializable

public class LetExpression
extends Assignation
implements Instr

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
 void process(XPathContext context)
          Process this expression as an instruction, writing results to the current outputter
 TailCall processLeavingTail(XPathContext context)
          Process the instruction, optionally returning an uncompleted tail call to be invoked by the caller
 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, getSourceLocator, getSpecialProperties, setLineNumber, typeError
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface net.sf.saxon.instruct.Locatable
getSourceLocator
 

Constructor Detail

LetExpression

public LetExpression()
Method Detail

analyze

public Expression analyze(StaticContext env)
                   throws XPathException
Type-check the expression

Specified by:
analyze in interface 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
XPathException

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

process

public void process(XPathContext context)
             throws javax.xml.transform.TransformerException
Process this expression as an instruction, writing results to the current outputter

Specified by:
process in interface Instr
Parameters:
context - The dynamic context, giving access to the current node, the current variables, etc.
javax.xml.transform.TransformerException

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws javax.xml.transform.TransformerException
Process the instruction, optionally returning an uncompleted tail call to be invoked by the caller

Specified by:
processLeavingTail in interface Instr
Parameters:
context - The dynamic context, giving access to the current node, the current variables, etc.
javax.xml.transform.TransformerException

getItemType

public ItemType getItemType()
Determine the data type of the items returned by the expression, if possible

Specified by:
getItemType in interface Expression
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)

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

Specified by:
display in interface Expression
Parameters:
level - indentation level for this expression