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, Container, 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()

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(Optimizer opt, StaticContext env, ItemType contextItemType) Convert where clause, if possible, to a predicate.
void	display(int level, PrintStream out, Configuration config) 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
int	getPositionVariableNameCode()
int	getRequiredSlots() Get the number of slots required.
SequenceIterator	iterate(XPathContext context) Iterate over the sequence of values
int	markTailFunctionCalls(int nameCode, int arity) Mark tail function calls: only possible if the for expression iterates zero or one times.
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Optimize the expression
void	process(XPathContext context) Process this expression as an instruction, writing results to the current outputter
void	setAction(Expression action) Add the "return" or "satisfies" expression, and fix up all references to the range variable that occur within that expression
void	setPositionVariable(RangeVariableDeclaration decl) Set the reference to the position variable (XQuery only)
void	setSlotNumber(int nr) Set the slot number for the range variable
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression

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

evaluateVariable, getAction, getLocalSlotNumber, getSequence, getVariableDeclaration, getVariableFingerprint, getVariableName, getVariableNameCode, isAssignable, isGlobal, iterateSubExpressions, promote, replaceSubExpression, setSequence, setVariableDeclaration, simplify, suppressValidation

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

adoptChildExpression, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getContainingProcedure, getDependencies, getExecutable, getHostLanguage, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, resetStaticProperties, setLocationId, setParentExpression, setParentExpression

Methods inherited from class java.lang.Object

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

Constructor Detail

ForExpression

public ForExpression()

Method Detail

setPositionVariable

public void setPositionVariable(RangeVariableDeclaration decl)

Set the reference to the position variable (XQuery only)

getPositionVariableNameCode

public int getPositionVariableNameCode()

setAction

public void setAction(Expression action)

Description copied from class: Assignation

Add the "return" or "satisfies" expression, and fix up all references to the range variable that occur within that expression

Overrides:

setAction in class Assignation

Parameters:

action - the expression that occurs after the "return" keyword of a "for" expression, the "satisfies" keyword of "some/every", or the ":=" operator of a "let" expression.

This method must be called after calling setVariableDeclaration()

setSlotNumber

public void setSlotNumber(int nr)

Set the slot number for the range variable

Overrides:

setSlotNumber in class Assignation

getRequiredSlots

public int getRequiredSlots()

Get the number of slots required. Normally 1, except for a FOR expression with an AT clause, where it is 2.

Overrides:

getRequiredSlots in class Assignation

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression

Overrides:

typeCheck in class Expression

Parameters:

env - the static context of the expression

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:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           ItemType contextItemType)
                    throws XPathException

Optimize the expression

Overrides:

optimize in class Expression

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 expression

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:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

convertWhereToPredicate

public Expression convertWhereToPredicate(Optimizer opt,
                                          StaticContext env,
                                          ItemType contextItemType)
                                   throws XPathException

Convert where clause, if possible, to a predicate. Returns the converted expression if modified, or null otherwise

Throws:

XPathException

markTailFunctionCalls

public int markTailFunctionCalls(int nameCode,
                                 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

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

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

Throws:

XPathException

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

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 -

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

display

public void display(int level,
                    PrintStream out,
                    Configuration config)

Diagnostic print of expression structure

Specified by:

display in class Expression

Parameters:

level - indentation level for this expression

out - Output destination