net.sf.saxon.instruct

Class Instruction

Implemented Interfaces:
SourceLocator, EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator, TailCallReturner
Known Direct Subclasses:
AnalyzeString, ApplyImports, ApplyTemplates, Block, CallTemplate, Choose, CopyOf, Doctype, ForEach, ForEachGroup, GeneralVariable, Message, ParentNodeConstructor, ResultDocument, SimpleNodeConstructor, TraceWrapper, UseAttributeSets, While

public abstract class Instruction
extends Expression
implements SourceLocator, TailCallReturner

Abstract superclass for all instructions in the compiled stylesheet. This represents a compiled instruction, and as such, the minimum information is retained from the original stylesheet.
Note: this class implements SourceLocator: that is, it can identify where in the stylesheet the source instruction was located.

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

Instruction()
Constructor

Method Summary

protected static ParameterSet
assembleParams(XPathContext context, WithParam[] actualParams)
Assemble a ParameterSet.
protected static ParameterSet
assembleTunnelParams(XPathContext context, WithParam[] actualParams)
Assemble a ParameterSet.
int
computeCardinality()
Get the cardinality of the sequence returned by evaluating this instruction
int
computeSpecialProperties()
Get the static properties of this expression (other than its type).
boolean
createsNewNodes()
Determine whether this instruction creates new nodes.
protected static XPathException
dynamicError(SourceLocator loc, XPathException error, XPathContext context)
Construct an exception with diagnostic information.
CharSequence
evaluateAsString(XPathContext context)
Evaluate an expression as a String.
Item
evaluateItem(XPathContext context)
Evaluate an expression as a single item.
int
getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
InstructionInfo
getInstructionInfo()
Get InstructionInfo for this expression
int
getInstructionNameCode()
Get the namecode of the instruction for use in diagnostics
ItemType
getItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instruction
SourceLocator
getSourceLocator()
Get a SourceLocator identifying the location of this instruction
boolean
isXSLT()
Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)
SequenceIterator
iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence.
void
process(XPathContext context)
Process the instruction, without returning any tail calls
abstract TailCall
processLeavingTail(XPathContext context)
ProcessLeavingTail: called to do the real work of this instruction.
Expression
promote(PromotionOffer offer)
Offer promotion for this subexpression.
protected void
promoteInst(PromotionOffer offer)
Handle promotion offers, that is, non-local tree rewrites.
abstract Expression
simplify(ExpressionVisitor visitor)
Simplify an expression.

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Constructor Details

Instruction

public Instruction()
Constructor

Method Details

assembleParams

protected static ParameterSet assembleParams(XPathContext context,
                                             WithParam[] actualParams)
            throws XPathException
Assemble a ParameterSet. Method used by instructions that have xsl:with-param children. This method is used for the non-tunnel parameters.
Parameters:
context - the XPath dynamic context
actualParams - the set of with-param parameters that specify tunnel="no"
Returns:
a ParameterSet

assembleTunnelParams

protected static ParameterSet assembleTunnelParams(XPathContext context,
                                                   WithParam[] actualParams)
            throws XPathException
Assemble a ParameterSet. Method used by instructions that have xsl:with-param children. This method is used for the tunnel parameters.
Parameters:
context - the XPath dynamic context
actualParams - the set of with-param parameters that specify tunnel="yes"
Returns:
a ParameterSet

computeCardinality

public int computeCardinality()
Get the cardinality of the sequence returned by evaluating this instruction
Overrides:
computeCardinality in interface Expression
Returns:
the static cardinality

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 interface Expression
Returns:
a set of flags indicating static properties of this expression

createsNewNodes

public boolean createsNewNodes()
Determine whether this instruction creates new nodes. This implementation returns a default value of false
Returns:
true if the instruction creates new nodes (or if it can't be proved that it doesn't)

dynamicError

protected static XPathException dynamicError(SourceLocator loc,
                                             XPathException error,
                                             XPathContext context)
Construct an exception with diagnostic information. Note that this method returns the exception, it does not throw it: that is up to the caller.
Parameters:
loc - the location of the error
error - The exception containing information about the error
context - The controller of the transformation
Returns:
an exception based on the supplied exception, but with location information added relating to this instruction

evaluateAsString

public final CharSequence evaluateAsString(XPathContext context)
            throws XPathException
Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.
Overrides:
evaluateAsString in interface Expression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".
Throws:
XPathException - if any dynamic error occurs evaluating the expression

evaluateItem

public Item evaluateItem(XPathContext context)
            throws XPathException
Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in interface Expression
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

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 prefered. For instructions this is the process() method.
Overrides:
getImplementationMethod in interface Expression

getInstructionInfo

public InstructionInfo getInstructionInfo()
Get InstructionInfo for this expression
Specified by:
getInstructionInfo in interface InstructionInfoProvider
Overrides:
getInstructionInfo in interface Expression

getInstructionNameCode

public int getInstructionNameCode()
Get the namecode of the instruction for use in diagnostics
Returns:
a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

getItemType

public ItemType getItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instruction
Overrides:
getItemType in interface Expression
Parameters:
th - the type hierarchy cache
Returns:
the static item type of the instruction

getSourceLocator

public SourceLocator getSourceLocator()
Get a SourceLocator identifying the location of this instruction
Returns:
the location of this instruction in the source stylesheet or query

isXSLT

public boolean isXSLT()
Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)
Returns:
true for XSLT, false for XQuery

iterate

public SequenceIterator 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.
Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in interface 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 interface Expression
Parameters:
context - The dynamic context, giving access to the current node, the current variables, etc.

processLeavingTail

public abstract TailCall processLeavingTail(XPathContext context)
            throws XPathException
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
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.

promote

public Expression promote(PromotionOffer offer)
            throws XPathException
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. This method is always called at compile time.
Overrides:
promote in interface 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
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

promoteInst

protected void promoteInst(PromotionOffer offer)
            throws XPathException
Handle promotion offers, that is, non-local tree rewrites.
Parameters:
offer - The type of rewrite being offered
Throws:
XPathException -

simplify

public abstract 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 interface Expression
Parameters:
visitor - an expression visitor
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting