net.sf.saxon.expr.flwor
Class FLWORExpression

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.flwor.FLWORExpression

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

public class FLWORExpression
extends Expression

This class represents a FLWOR expression, evaluated using tuple streams

See Also:

Serialized Form

Field Summary

List<Clause>	clauses
Expression	returnClause

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD

Constructor Summary

FLWORExpression(List<Clause> clauses, Expression returnClause)

Method Summary

void	checkForUpdatingSubexpressions() Check to ensure that this expression does not contain any inappropriate updating subexpressions.
protected int	computeCardinality() Compute the static cardinality of this expression
Expression	copy() Copy an expression.
void	evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
List<Clause>	getClauseList() Get the list of clauses of the FLWOR expression, in the order they are written.
int	getEvaluationMethod()
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items returned by the expression.
Expression	getReturnClause() Get the return clause of the FLWOR expression
boolean	hasLoopingSubexpression(Expression child) Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
boolean	hasLoopingVariableReference(Binding binding, Expression reference)
boolean	hasVariableBinding(Binding binding) Determine whether a given variable binding belongs to this FLWOR expression
boolean	isUpdatingExpression() Determine whether this is an updating expression as defined in the XQuery update specification
SequenceIterator<? extends Item>	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
Iterator<Expression>	iterateSubExpressions() Get the immediate sub-expressions of this expression.
Expression	optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.
void	process(XPathContext context) Process the instruction, without returning any tail calls
Expression	promote(PromotionOffer offer, Expression parent) Promote this expression if possible
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
void	replaceVariable(Optimizer opt, Expression seq) Replace all references to the variable bound by this let expression, that occur within the action expression, with the given expression
Expression	simplify(ExpressionVisitor visitor) Simplify an expression.
String	toString() Display the expression as a string
Expression	typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform type checking of an expression and its subexpressions.

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getExpressionName, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isSubtreeExpression, isVacuousExpression, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError

Methods inherited from class java.lang.Object

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

Field Detail

clauses

public List<Clause> clauses

returnClause

public Expression returnClause

Constructor Detail

FLWORExpression

public FLWORExpression(List<Clause> clauses,
                       Expression returnClause)

Method Detail

getClauseList

public List<Clause> getClauseList()

Get the list of clauses of the FLWOR expression, in the order they are written. This excludes the return clause

Returns:

the list of clauses

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)

Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly

Overrides:

hasLoopingSubexpression in class Expression

Parameters:

child - the immediate subexpression

Returns:

true if the child expression is evaluated repeatedly

getReturnClause

public Expression getReturnClause()

Get the return clause of the FLWOR expression

Returns:

the expression contained in the return clause

hasVariableBinding

public boolean hasVariableBinding(Binding binding)

Determine whether a given variable binding belongs to this FLWOR expression

Overrides:

hasVariableBinding in class Expression

Parameters:

binding - the binding being sought

Returns:

true if this binding belongs to one of the clauses of this FLWOR expression

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Overrides:

simplify in class Expression

Parameters:

visitor - an expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType contextItemType)
                     throws XPathException

Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextItemType - 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 to Type.ITEM_TYPE

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)

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the items returned by the expression.

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

Returns:

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

computeCardinality

protected int computeCardinality()

Compute the static cardinality of this expression

Specified by:

computeCardinality in class Expression

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

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Get the immediate sub-expressions of this expression.

Overrides:

iterateSubExpressions in class Expression

Returns:

an iterator containing the sub-expressions of this expression

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException

Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.

Overrides:

checkForUpdatingSubexpressions in class Expression

Throws:

XPathException - if the expression has a non-permitted updateing subexpression

isUpdatingExpression

public boolean isUpdatingExpression()

Determine whether this is an updating expression as defined in the XQuery update specification

Overrides:

isUpdatingExpression in class Expression

Returns:

true if this is an updating expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

replaceVariable

public void replaceVariable(Optimizer opt,
                            Expression seq)
                     throws XPathException

Replace all references to the variable bound by this let expression, that occur within the action expression, with the given expression

Parameters:

opt - The optimizer

seq - the expression

Throws:

XPathException - if an error occurs

explain

public void explain(ExpressionPresenter out)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

explain in class Expression

Parameters:

out - the expression presenter used to display the structure

copy

public Expression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

promote

public Expression promote(PromotionOffer offer,
                          Expression parent)
                   throws XPathException

Promote this expression if possible

Overrides:

promote in class Expression

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

parent - the containing expression in the expression tree

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

getEvaluationMethod

public int getEvaluationMethod()

Overrides:

getEvaluationMethod in class Expression

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ExpressionVisitor.ContextItemType contextItemType)
                    throws XPathException

Description copied from class: Expression

Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

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:

optimize in class Expression

Parameters:

visitor - an expression visitor

contextItemType - 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 to Type.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)

iterate

public SequenceIterator<? extends Item> iterate(XPathContext context)
                                         throws XPathException

Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Overrides:

iterate in class Expression

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

process

public void process(XPathContext context)
             throws XPathException

Process the instruction, without returning any tail calls

Overrides:

process in class Expression

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException - if a dynamic error occurs

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:

evaluatePendingUpdates in class Expression

Parameters:

context - the XPath dynamic evaluation context

pul - the pending update list to which the results should be written

Throws:

XPathException - if evaluation fails

UnsupportedOperationException - if the expression is not an updating expression

toString

public String toString()

Display the expression as a string

Overrides:

toString in class Expression

Returns:

a representation of the expression as a string

hasLoopingVariableReference

public boolean hasLoopingVariableReference(Binding binding,
                                           Expression reference)