Package net.sf.saxon.instruct

Class While

java.lang.Object

net.sf.saxon.expr.ComputedExpression

net.sf.saxon.instruct.Instruction

net.sf.saxon.instruct.While

All Implemented Interfaces:

Serializable, SourceLocator, Container, Expression, TailCallReturner, InstructionInfoProvider

public class While
extends Instruction

Handler for saxon:while elements in stylesheet.
The saxon:while element has a mandatory attribute test, a boolean expression. The content is output repeatedly so long as the test condition is true.

See Also:

• Serialized Form

Field Summary

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

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Constructors

Constructor	Description
While(Expression test, Expression action)

Method Summary

Modifier and Type	Method	Description
final boolean	createsNewNodes()	Determine whether this instruction creates new nodes.
void	display(int level, PrintStream out, Configuration config)	Diagnostic print of expression structure.
Expression	getActionExpression()	Get the action expression (the content of the for-each)
int	getInstructionNameCode()	Get the name of this instruction for diagnostic and tracing purposes
ItemType	getItemType(TypeHierarchy th)	Get the item type of the items returned by evaluating this instruction
Iterator	iterateSubExpressions()	Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType)	Perform optimisation of an expression and its subexpressions.
TailCall	processLeavingTail(XPathContext context)	ProcessLeavingTail: called to do the real work of this instruction.
protected void	promoteInst(PromotionOffer offer)	Handle promotion offers, that is, non-local tree rewrites.
boolean	replaceSubExpression(Expression original, Expression replacement)	Replace one subexpression by a replacement subexpression
Expression	simplify(StaticContext env)	Simplify an expression.
Expression	typeCheck(StaticContext env, ItemType contextItemType)	Perform type checking of an expression and its subexpressions.

Methods inherited from class net.sf.saxon.instruct.Instruction

appendItem, assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, evaluateAsString, evaluateItem, getImplementationMethod, getInstructionInfo, getSourceLocator, isXSLT, iterate, process, promote

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError

Methods inherited from class java.lang.Object

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

Methods inherited from interface javax.xml.transform.SourceLocator

getColumnNumber, getLineNumber, getPublicId, getSystemId

Constructor Details

While

public While(Expression test,
 Expression action)

Method Details

getInstructionNameCode

public int getInstructionNameCode()

Get the name of this instruction for diagnostic and tracing purposes

Overrides:

getInstructionNameCode in class Instruction

Returns:

the string "saxon:while"

getActionExpression

public Expression getActionExpression()

Get the action expression (the content of the for-each)

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).

Specified by:

simplify in interface Expression

Specified by:

simplify in class Instruction

Parameters:

env - the static context

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

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

Description copied from interface: Expression

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 parent pointer and 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.

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:

XPathException

optimize

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

Description copied from interface: 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.

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:

XPathException

getItemType

public ItemType getItemType(TypeHierarchy th)

Get the item type of the items returned by evaluating this instruction

Specified by:

getItemType in interface Expression

Overrides:

getItemType in class Instruction

Parameters:

th -

Returns:

the static item type of the instruction

promoteInst

protected void promoteInst(PromotionOffer offer)
                    throws XPathException

Handle promotion offers, that is, non-local tree rewrites.

Overrides:

promoteInst in class Instruction

Parameters:

offer - The type of rewrite being offered

Throws:

XPathException

createsNewNodes

public final boolean createsNewNodes()

Determine whether this instruction creates new nodes. This implementation returns true if the "action" creates new nodes. (Nodes created by the condition can't contribute to the result).

Overrides:

createsNewNodes in class Instruction

iterateSubExpressions

public Iterator iterateSubExpressions()

Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
 Expression replacement)

Replace one subexpression by a replacement subexpression

Specified by:

replaceSubExpression in interface Container

Overrides:

replaceSubExpression in class ComputedExpression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

Description copied from class: Instruction

ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.

Specified by:

processLeavingTail in interface TailCallReturner

Specified by:

processLeavingTail in class Instruction

Parameters:

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

Returns:

null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.

Throws:

XPathException

display

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

Diagnostic print of expression structure. The expression is written to the System.err output stream

Parameters:

level - indentation level for this expression

out -

config -