net.sf.saxon.instruct
Class Instruction

java.lang.Object
  |
  +--net.sf.saxon.expr.ComputedExpression
        |
        +--net.sf.saxon.instruct.Instruction
All Implemented Interfaces:
Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator
Direct Known Subclasses:
AnalyzeString, ApplyImports, ApplyTemplates, CallTemplate, Choose, CopyOf, DeferredError, ForEach, ForEachGroup, GeneralVariable, InstructionWithChildren, TraceWrapper, While

public abstract class Instruction
extends ComputedExpression
implements javax.xml.transform.SourceLocator

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.

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
Instruction()
          Constructor
 
Method Summary
abstract  Expression analyze(StaticContext env, ItemType contextItemType)
          Perform static analysis of an expression and its subexpressions.
static void appendItem(Item it, SequenceReceiver out, int locationId)
          Static method to append an item that results from evaluating an expression to the current result receiver.
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).
protected static XPathException dynamicError(javax.xml.transform.SourceLocator loc, XPathException error, XPathContext context)
          Construct an exception with diagnostic information.
protected  XPathException dynamicError(java.lang.String message, Controller controller)
          Raise a dynamic error
 boolean effectiveBooleanValue(XPathContext context)
          Get the effective boolean value of the expression.
 java.lang.String 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()
          Get the item type of the items returned by evaluating this instruction
 javax.xml.transform.SourceLocator getSourceLocator()
          Get a SourceLocator identifying the location of this instruction
 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(StaticContext env)
          Simplify an expression.
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, computeDependencies, computeStaticProperties, dynamicError, dynamicError, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getIntrinsicDependencies, getLineNumber, getLocationId, getParentExpression, getPublicId, getSpecialProperties, getSystemId, iterateSubExpressions, markTailFunctionCalls, resetStaticProperties, setLocationId, setParentExpression, 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
 
Methods inherited from interface net.sf.saxon.expr.Expression
display
 

Constructor Detail

Instruction

public Instruction()
Constructor

Method Detail

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.

Specified by:
getImplementationMethod in interface Expression
Overrides:
getImplementationMethod in class ComputedExpression

getInstructionNameCode

public int getInstructionNameCode()
Get the namecode of the instruction for use in diagnostics


getItemType

public ItemType getItemType()
Get the item type of the items returned by evaluating this instruction

Specified by:
getItemType in interface Expression
Returns:
the static item type of the instruction

computeCardinality

public int computeCardinality()
Get the cardinality of the sequence returned by evaluating this instruction

Specified by:
computeCardinality in class ComputedExpression
Returns:
the static cardinality

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.

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.
XPathException

process

public void process(XPathContext context)
             throws XPathException
Process the instruction, without returning any tail calls

Specified by:
process in interface Expression
Overrides:
process in class ComputedExpression
Parameters:
context - The dynamic context, giving access to the current node, the current variables, etc.
XPathException

getSourceLocator

public javax.xml.transform.SourceLocator getSourceLocator()
Get a SourceLocator identifying the location of this instruction


dynamicError

protected static XPathException dynamicError(javax.xml.transform.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:
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

dynamicError

protected XPathException dynamicError(java.lang.String message,
                                      Controller controller)
Raise a dynamic error

Parameters:
message - An English text error message
controller - The controller of the transformation
Returns:
an exception containing details of the dynamic error

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.

XPathException

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.

XPathException

simplify

public abstract Expression simplify(StaticContext env)
                             throws XPathException
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Specified by:
simplify in interface Expression
Overrides:
simplify in class ComputedExpression
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

analyze

public abstract Expression analyze(StaticContext env,
                                   ItemType contextItemType)
                            throws XPathException
Perform static analysis of an expression and its subexpressions.

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 will only be accurately known if they have been explicitly declared.

Specified by:
analyze in interface 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:
XPathException - if an error is discovered during this phase (typically a type error)

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 class ComputedExpression
Returns:
a set of flags indicating static properties of this expression

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

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.

Specified by:
promote in interface Expression
Overrides:
promote in class ComputedExpression
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

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 Expression
Overrides:
evaluateItem in class ComputedExpression
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

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 Expression
Overrides:
iterate in class ComputedExpression
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

evaluateAsString

public final java.lang.String 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.

Specified by:
evaluateAsString in interface Expression
Overrides:
evaluateAsString in class ComputedExpression
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
java.lang.ClassCastException - if the result type of the expression is not xs:string?

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Specified by:
effectiveBooleanValue in interface Expression
Overrides:
effectiveBooleanValue in class ComputedExpression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the effective boolean value
Throws:
XPathException - if any dynamic error occurs evaluating the expression

getInstructionInfo

public InstructionInfo getInstructionInfo()
Description copied from class: ComputedExpression
Get InstructionInfo for this expression

Specified by:
getInstructionInfo in interface InstructionInfoProvider
Overrides:
getInstructionInfo in class ComputedExpression

appendItem

public static void appendItem(Item it,
                              SequenceReceiver out,
                              int locationId)
                       throws XPathException
Static method to append an item that results from evaluating an expression to the current result receiver. The method checks to see whether the item returned from the expression is actually a function-call-package representing the result of a tail call optimization; if so, the tail function calls are complete and the final result is passed on.

Parameters:
it - the item: possibly a FunctionCallPackage
out - the Receiver
Throws:
XPathException