net.sf.saxon.expr
Class ForExpression

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.Assignation
          net.sf.saxon.expr.ForExpression

All Implemented Interfaces:

Serializable, SourceLocator, Binding, EvaluableItem, SequenceIterable, InstructionInfoProvider

public class ForExpression
extends Assignation

A ForExpression maps an expression over a sequence. This version works with range variables, it doesn't change the context information

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

ForExpression()
Create a "for" expression (for $x at $p in SEQUENCE return ACTION)

Method Summary

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 expression
Expression	convertWhereToPredicate(ExpressionVisitor visitor, ItemType contextItemType) Convert where clause, if possible, to a predicate.
Expression	copy() Copy an expression.
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items returned by the expression, if possible
StructuredQName	getPositionVariableName() Get the name of the position variable
int	getRequiredSlots() Get the number of slots required.
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
SequenceIterator	iterate(XPathContext context) Iterate over the sequence of values
EventIterator	iterateEvents(XPathContext context) Deliver the result of the expression as a sequence of events.
int	markTailFunctionCalls(StructuredQName qName, int arity) Mark tail function calls: only possible if the for expression iterates zero or one times.
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Optimize the expression
void	process(XPathContext context) Process this expression as an instruction, writing results to the current outputter
void	setPositionVariable(PositionVariable decl) Set the reference to the position variable (XQuery only)
void	setSlotNumber(int nr) Set the slot number for the range variable
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Type-check the expression

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

addToPathMap, evaluateVariable, getAction, getLocalSlotNumber, getRequiredType, getSequence, getVariableName, getVariableQName, isAssignable, isGlobal, iterateSubExpressions, promote, refineTypeInformation, replaceSubExpression, setAction, setRequiredType, setSequence, setVariableQName, simplify, suppressValidation

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

adoptChildExpression, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, implementsStaticTypeCheck, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, toString

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ForExpression

public ForExpression()

Create a "for" expression (for $x at $p in SEQUENCE return ACTION)

Method Detail

setPositionVariable

public void setPositionVariable(PositionVariable decl)

Set the reference to the position variable (XQuery only)

Parameters:

decl - the range variable declaration for the position variable

getPositionVariableName

public StructuredQName getPositionVariableName()

Get the name of the position variable

Returns:

the name of the position variable ("at $p") if there is one, or null if not

setSlotNumber

public void setSlotNumber(int nr)

Set the slot number for the range variable

Overrides:

setSlotNumber in class Assignation

Parameters:

nr - the slot number allocated to the range variable on the local stack frame. This implicitly allocates the next slot number to the position variable if there is one.

getRequiredSlots

public int getRequiredSlots()

Get the number of slots required.

Overrides:

getRequiredSlots in class Assignation

Returns:

normally 1, except for a FOR expression with an AT clause, where it is 2.

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression

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)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
                    throws XPathException

Optimize the expression

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)

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

convertWhereToPredicate

public Expression convertWhereToPredicate(ExpressionVisitor visitor,
                                          ItemType contextItemType)
                                   throws XPathException

Convert where clause, if possible, to a predicate.

Parameters:

visitor - the expression visitor

contextItemType - the item type of the context item

Returns:

the converted expression if modified, or null otherwise

Throws:

XPathException

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

markTailFunctionCalls

public int markTailFunctionCalls(StructuredQName qName,
                                 int arity)

Mark tail function calls: only possible if the for expression iterates zero or one times. (This arises in XSLT/XPath, which does not have a LET expression, so FOR gets used instead)

Overrides:

markTailFunctionCalls in class Expression

Parameters:

qName - the name of the function

arity - the arity (number of parameters) of the function

Returns:

0 if no tail call was found; 1 if a tail call on a different function was found; 2 if a tail recursive call was found and if this call accounts for the whole of the value.

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. This implementation provides both iterate() and process() methods natively.

Overrides:

getImplementationMethod in class Expression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

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.

Overrides:

checkPermittedContents in class Expression

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 type

env - the static context

whole - 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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the sequence of values

Specified by:

iterate in interface SequenceIterable

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

iterateEvents

public EventIterator iterateEvents(XPathContext context)
                            throws XPathException

Deliver the result of the expression as a sequence of events.

Overrides:

iterateEvents in class Expression

Parameters:

context - The dynamic evaluation context

Returns:

the result of the expression as an iterator over a sequence of PullEvent objects

Throws:

XPathException - if a dynamic error occurs during expression evaluation

process

public void process(XPathContext context)
             throws XPathException

Process this expression as an instruction, writing results to the current outputter

Overrides:

process in class Expression

Parameters:

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

Throws:

XPathException

getItemType

public ItemType getItemType(TypeHierarchy th)

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

Specified by:

getItemType in class Expression

Parameters:

th - the type hierarchy cache

Returns:

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

computeCardinality

public int computeCardinality()

Determine the static cardinality of the 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

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