net.sf.saxon.expr.instruct
Class TraceExpression

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.instruct.Instruction
          extended by net.sf.saxon.expr.instruct.TraceExpression
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, TailCallReturner, InstructionInfo, Locator

public class TraceExpression
extends Instruction
implements InstructionInfo

A wrapper expression used to trace expressions in XPath and XQuery.

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD
 
Constructor Summary
TraceExpression(Expression child)
          Create a trace expression that traces execution of a given child expression
 
Method Summary
 void checkForUpdatingSubexpressions()
          Check to ensure that this expression does not contain any inappropriate updating subexpressions.
 int computeDependencies()
          Get the static properties of this expression (other than its type).
 Expression copy()
          Copy an expression.
 boolean createsNewNodes()
          Determine whether this instruction creates new nodes.
 Item evaluateItem(XPathContext context)
          Evaluate an expression as a single item.
 void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul)
          Evaluate an updating expression, adding the results to a Pending Update List.
 void explain(ExpressionPresenter out)
          Diagnostic print of expression structure.
 int getCardinality()
          Determine the static cardinality of the expression.
 Expression getChildExpression()
           
 int getColumnNumber(long locationId)
          Get the column number within the document, entity, or module containing a particular location
 int getConstructType()
          Get the construct type.
 int getDependencies()
          Determine which aspects of the context the expression depends on.
 int getImplementationMethod()
          An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
 InstructionInfo getInstructionInfo()
          Get the InstructionInfo details about the construct.
 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
 int getLineNumber(long locationId)
          Get the line number of the expression being traced.
 NamespaceResolver getNamespaceResolver()
          Get the namespace resolver to supply the namespace context of the instruction that is being traced
 StructuredQName getObjectName()
          Get a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc.
 Iterator<String> getProperties()
          Get an iterator over all the properties available.
 Object getProperty(String name)
          Get a named property of the instruction/expression
 String getSystemId(long locationId)
          Get the system identifier (that is the base URI) of the static context of the expression being traced.
 boolean isUpdatingExpression()
          Determine whether this is an updating expression as defined in the XQuery update specification
 boolean isVacuousExpression()
          Determine whether this is a vacuous expression as defined in the XQuery update specification
 SequenceIterator<Item> iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 Iterator<Expression> iterateSubExpressions()
          Get the immediate sub-expressions of this expression.
 Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 TailCall processLeavingTail(XPathContext context)
          Execute this instruction, with the possibility of returning tail calls if there are any.
 Expression promote(PromotionOffer offer, Expression parent)
          Offer promotion for this subexpression.
 boolean replaceSubExpression(Expression original, Expression replacement)
          Replace one subexpression by a replacement subexpression
 void setConstructType(int type)
          Set the type of construct.
 void setNamespaceResolver(NamespaceResolver resolver)
          Set the namespace context for the instruction being traced.
 void setObjectName(StructuredQName qName)
          Set a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc.
 void setProperty(String name, Object value)
          Set a named property of the instruction/expression
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression.
 Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
          Perform type checking of an expression and its subexpressions.
 
Methods inherited from class net.sf.saxon.expr.instruct.Instruction
assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, evaluateAsString, getExpressionName, getInstructionName, getIteratorFromProcessMethod, getSourceLocator, isXSLT, process, promoteInst
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkPermittedContents, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, explain, getColumnNumber, getContainer, getEvaluationMethod, getExecutable, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeError
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface net.sf.saxon.trace.InstructionInfo
getLineNumber, getSystemId
 
Methods inherited from interface org.xml.sax.Locator
getColumnNumber, getPublicId
 
Methods inherited from interface javax.xml.transform.SourceLocator
getColumnNumber, getPublicId
 

Constructor Detail

TraceExpression

public TraceExpression(Expression child)
Create a trace expression that traces execution of a given child expression

Parameters:
child - the expression to be traced. This will be available to the TraceListener as the value of the "expression" property of the InstructionInfo.
Method Detail

setConstructType

public void setConstructType(int type)
Set the type of construct. This will generally be a constant in class Location

Parameters:
type - an integer code for the type of construct being traced

getConstructType

public int getConstructType()
Get the construct type. This will generally be a constant in class Location

Specified by:
getConstructType in interface InstructionInfo
Overrides:
getConstructType in class Instruction
Returns:
the type of expression, as enumerated in class Location

setNamespaceResolver

public void setNamespaceResolver(NamespaceResolver resolver)
Set the namespace context for the instruction being traced. This is needed if the tracelistener wants to evaluate XPath expressions in the context of the current instruction

Parameters:
resolver - The namespace resolver, or null if none is needed

getNamespaceResolver

public NamespaceResolver getNamespaceResolver()
Get the namespace resolver to supply the namespace context of the instruction that is being traced

Returns:
the namespace resolver, or null if none is in use

setObjectName

public void setObjectName(StructuredQName qName)
Set a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.

Parameters:
qName - the name of the object, or null if not applicable

getObjectName

public StructuredQName getObjectName()
Get a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.

Specified by:
getObjectName in interface InstructionInfo
Overrides:
getObjectName in class Expression
Returns:
the name of the object, or null if not applicable

setProperty

public void setProperty(String name,
                        Object value)
Set a named property of the instruction/expression

Parameters:
name - the name of the property
value - the value of the property

getProperty

public Object getProperty(String name)
Get a named property of the instruction/expression

Specified by:
getProperty in interface InstructionInfo
Overrides:
getProperty in class Expression
Parameters:
name - the name of the property
Returns:
the value of the property

getProperties

public Iterator<String> getProperties()
Get an iterator over all the properties available. The values returned by the iterator will be of type String, and each string can be supplied as input to the getProperty() method to retrieve the value of the property.

Specified by:
getProperties in interface InstructionInfo
Overrides:
getProperties in class Expression
Returns:
an iterator over the properties.

getInstructionInfo

public InstructionInfo getInstructionInfo()
Get the InstructionInfo details about the construct. This is to satisfy the InstructionInfoProvider interface.

Returns:
the instruction details

getSystemId

public String getSystemId(long locationId)
Get the system identifier (that is the base URI) of the static context of the expression being traced. This returns the same result as getSystemId(), it is provided to satisfy the LocationProvider interface.

Specified by:
getSystemId in interface LocationProvider
Overrides:
getSystemId in class Expression
Parameters:
locationId - not used
Returns:
the URI of the module containing the expression

getLineNumber

public int getLineNumber(long locationId)
Get the line number of the expression being traced. This returns the same result as getLineNumber(), it is provided to satisfy the LocationProvider interface.

Specified by:
getLineNumber in interface LocationProvider
Overrides:
getLineNumber in class Expression
Parameters:
locationId - not used
Returns:
the line number of the expression within its module

getColumnNumber

public int getColumnNumber(long locationId)
Description copied from interface: LocationProvider
Get the column number within the document, entity, or module containing a particular location

Specified by:
getColumnNumber in interface LocationProvider
Overrides:
getColumnNumber in class Expression
Parameters:
locationId - identifier of the location in question (as passed down the Receiver pipeline)
Returns:
the column number within the document, entity, or module, or -1 if this is not available

copy

public Expression copy()
Description copied from class: Expression
Copy an expression. This makes a deep copy.

Specified by:
copy in class Expression
Returns:
the copy of the original expression

isUpdatingExpression

public boolean isUpdatingExpression()
Determine whether this is an updating expression as defined in the XQuery update specification

Overrides:
isUpdatingExpression in class Expression
Returns:
true if this is an updating expression

isVacuousExpression

public boolean isVacuousExpression()
Determine whether this is a vacuous expression as defined in the XQuery update specification

Overrides:
isVacuousExpression in class Expression
Returns:
true if this expression is vacuous

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException
Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.

Overrides:
checkForUpdatingSubexpressions in class Expression
Throws:
XPathException - if the expression has a non-permitted updating subexpression

simplify

public 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.

Specified by:
simplify in class Instruction
Parameters:
visitor - an expression visitor
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType contextItemType)
                     throws XPathException
Description copied from class: 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 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.

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,
                           ExpressionVisitor.ContextItemType contextItemType)
                    throws XPathException
Description copied from class: 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.

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)

getImplementationMethod

public int getImplementationMethod()
Description copied from class: Instruction
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 class Instruction
Returns:
the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

promote

public Expression promote(PromotionOffer offer,
                          Expression parent)
                   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 class Instruction
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
parent - the parent of the subexpression
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

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException
Execute this instruction, with the possibility of returning tail calls if there are any. This outputs the trace information via the registered TraceListener, and invokes the instruction being traced.

Specified by:
processLeavingTail in interface TailCallReturner
Specified by:
processLeavingTail in class Instruction
Parameters:
context - the dynamic execution context
Returns:
either null, or a tail call that the caller must invoke on return
Throws:
XPathException

getItemType

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

Overrides:
getItemType in class Instruction
Parameters:
th - the type hierarchy cache
Returns:
the static item type of the instruction

getCardinality

public int getCardinality()
Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.

Overrides:
getCardinality in class Expression
Returns:
one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

getDependencies

public int getDependencies()
Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.DEPENDS_ON_CONTEXT_ITEM and StaticProperty.DEPENDS_ON_CURRENT_ITEM. The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression.

Overrides:
getDependencies in class Expression
Returns:
a set of bit-significant flags identifying the dependencies of the expression

createsNewNodes

public final boolean createsNewNodes()
Determine whether this instruction creates new nodes.

Overrides:
createsNewNodes in class Instruction
Returns:
true if the instruction creates new nodes (or if it can't be proved that it doesn't)

computeDependencies

public int computeDependencies()
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:
computeDependencies in class Expression
Returns:
a set of flags indicating static properties of this 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.

Overrides:
evaluateItem in class Instruction
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<Item> 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.

Overrides:
iterate in class Instruction
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

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()
Description copied from class: Expression
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Overrides:
iterateSubExpressions in class Expression
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

Overrides:
replaceSubExpression in class Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

getChildExpression

public Expression getChildExpression()

getInstructionNameCode

public int getInstructionNameCode()
Description copied from class: Instruction
Get the namecode of the instruction for use in diagnostics

Overrides:
getInstructionNameCode in class Instruction
Returns:
a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

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

evaluatePendingUpdates

public void evaluatePendingUpdates(XPathContext context,
                                   PendingUpdateList pul)
                            throws XPathException
Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException

Overrides:
evaluatePendingUpdates in class Expression
Parameters:
context - the XPath dynamic evaluation context
pul - the pending update list to which the results should be written
Throws:
XPathException - if evaluation fails


Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.