net.sf.saxon.expr.instruct

Class Choose

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.instruct.Instruction

net.sf.saxon.expr.instruct.Choose

All Implemented Interfaces:

TailCallReturner, IdentityComparable

public class Choose
extends Instruction

Compiled representation of an xsl:choose or xsl:if element in the stylesheet. Also used for typeswitch in XQuery.

Field Summary

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
Choose(Expression[] conditions, Expression[] actions) Construct an xsl:choose instruction

Method Summary

Methods

Modifier and Type	Method and Description
Iterable<Operand>	actions()
PathMap.PathMapNodeSet	addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.
void	atomizeActions() Atomize all the action expressions
void	checkForUpdatingSubexpressions() Check to ensure that this expression does not contain any updating subexpressions.
void	checkPermittedContents(SchemaType parentType, 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() Compute the cardinality of the sequence returned by evaluating this instruction
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
Iterable<Operand>	conditions()
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	export(ExpressionPresenter out) Diagnostic print of expression structure.
Expression	getAction(int i) Get i'th action to be performed
Operand	getActionOperand(int i) Get i'th action operand
Expression	getCondition(int i)
ExpressionCompiler	getExpressionCompiler() Return the compiler of the Choose expression
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
int	getInstructionNameCode() Get the name of this instruction for diagnostic and tracing purposes We assume that if there was only one condition then it was an xsl:if; this is not necessarily so, but it's adequate for tracing purposes.
ItemType	getItemType() Get the item type of the items returned by evaluating this instruction
int	getNumberOfConditions()
ChooseAdjunct	getStreamingAdjunct() Get a class that supports streamed evaluation of this expression
boolean	implementsStaticTypeCheck() Determine whether this expression implements its own method for static type checking
static boolean	isSingleBranchChoice(Expression exp) Test whether an expression is a single-branch choose, that is, an expression of the form if (condition) then exp else ()
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	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
EventIterator	iterateEvents(XPathContext context) Deliver the result of the expression as a sequence of events.
static Expression	makeConditional(Expression condition, Expression thenExp) Make a simple conditional expression (if (condition) then (thenExp) else ()
static Expression	makeConditional(Expression condition, Expression thenExp, Expression elseExp) Make a simple conditional expression (if (condition) then (thenExp) else (elseExp)
int	markTailFunctionCalls(StructuredQName qName, int arity) Mark tail-recursive calls on functions.
Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Perform optimisation of an expression and its subexpressions.
TailCall	processLeavingTail(XPathContext context) Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.
protected void	promoteChildren(PromotionOffer offer) Handle promotion offers, that is, non-local tree rewrites.
void	setAction(int i, Expression action)
void	setCondition(int i, Expression condition)
Expression	simplify() Simplify an expression.
int	size()
Expression	staticTypeCheck(SequenceType req, boolean backwardsCompatible, RoleDiagnostic role, ExpressionVisitor visitor) Static type checking for conditional expressions is delegated to the expression itself, and is performed separately on each branch of the conditional, so that dynamic checks are added only on those branches where the check is actually required.
String	toShortString() Produce a short string identifying the expression for use in error messages
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
Expression	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform type checking of an expression and its subexpressions.
Expression	unordered(boolean retainAllNodes, boolean forStreaming) Replace this expression by a simpler expression that delivers the results without regard to order.

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

assembleParams, assembleTunnelParams, dynamicError, evaluateAsString, getConstructType, getExpressionName, getInstructionName, getNetCost, getSourceLocator, isXSLT, main, process, toStreamingPattern

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

adoptChildExpression, checkedOperands, clearStreamabilityData, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLocation, getObjectName, getPackageData, getParentExpression, getPosture, getPostureAndSweepIfKnown, getProperties, getProperty, getRetainedStaticContext, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStreamability, getSweep, getSystemId, hasVariableBinding, identityHashCode, isCallOn, isCallOnSystemFunction, isIdentical, isSubtreeExpression, makeStreamingAdjunct, operandList, operandSparseList, optimizeChildren, optimizeForType, promote, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setFiltered, setFlattened, setLocation, setParentExpression, setPostureAndSweep, setRetainedStaticContext, setRetainedStaticContextLocally, setStaticProperty, simplifyChildren, suppressValidation, toPattern, typeCheckChildren, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

Choose

public Choose(Expression[] conditions,
      Expression[] actions)

Construct an xsl:choose instruction

Parameters:

conditions - the conditions to be tested, in order

actions - the actions to be taken when the corresponding condition is true

Method Detail

makeConditional

public static Expression makeConditional(Expression condition,
                         Expression thenExp,
                         Expression elseExp)

Make a simple conditional expression (if (condition) then (thenExp) else (elseExp)

Parameters:

condition - the condition to be tested

thenExp - the expression to be evaluated if the condition is true

elseExp - the expression to be evaluated if the condition is false

Returns:

the expression

makeConditional

public static Expression makeConditional(Expression condition,
                         Expression thenExp)

Make a simple conditional expression (if (condition) then (thenExp) else ()

Parameters:

condition - the condition to be tested

thenExp - the expression to be evaluated if the condition is true

Returns:

the expression

size

public int size()

isSingleBranchChoice

public static boolean isSingleBranchChoice(Expression exp)

Test whether an expression is a single-branch choose, that is, an expression of the form if (condition) then exp else ()

Parameters:

exp - the expression to be tested

Returns:

true if the expression is a choose expression and there is only one condition, so that the expression returns () if this condition is false

getNumberOfConditions

public int getNumberOfConditions()

getCondition

public Expression getCondition(int i)

setCondition

public void setCondition(int i,
                Expression condition)

conditions

public Iterable<Operand> conditions()

getActionOperand

public Operand getActionOperand(int i)

Get i'th action operand

Parameters:

i - the action number

Returns:

the i'th action to be evaluated when the corresponding condition is true

getAction

public Expression getAction(int i)

Get i'th action to be performed

Parameters:

i - the action number

Returns:

the i'th action to be evaluated when the corresponding condition is true

setAction

public void setAction(int i,
             Expression action)

actions

public Iterable<Operand> actions()

operands

public Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Specified by:

operands in class Instruction

Returns:

an iterator containing the sub-expressions of this expression

atomizeActions

public void atomizeActions()

Atomize all the action expressions

getInstructionNameCode

public int getInstructionNameCode()

Get the name of this instruction for diagnostic and tracing purposes We assume that if there was only one condition then it was an xsl:if; this is not necessarily so, but it's adequate for tracing purposes.

Overrides:

getInstructionNameCode in class Instruction

Returns:

a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

simplify

public Expression simplify()
                    throws XPathException

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

Overrides:

simplify in class Expression

Returns:

the simplified expression (or the original if unchanged, or if modified in-situ)

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                   ContextItemStaticInfo contextInfo)
                     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.

Overrides:

typeCheck in class Expression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

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)

implementsStaticTypeCheck

public boolean implementsStaticTypeCheck()

Determine whether this expression implements its own method for static type checking

Overrides:

implementsStaticTypeCheck in class Expression

Returns:

true - this expression has a non-trivial implementation of the staticTypeCheck() method

staticTypeCheck

public Expression staticTypeCheck(SequenceType req,
                         boolean backwardsCompatible,
                         RoleDiagnostic role,
                         ExpressionVisitor visitor)
                           throws XPathException

Static type checking for conditional expressions is delegated to the expression itself, and is performed separately on each branch of the conditional, so that dynamic checks are added only on those branches where the check is actually required. This also results in a static type error if any branch is incapable of delivering a value of the required type. One reason for this approach is to avoid doing dynamic type checking on a recursive function call as this prevents tail-call optimization being used.

Overrides:

staticTypeCheck in class Expression

Parameters:

req - the required type

backwardsCompatible - true if backwards compatibility mode applies

role - the role of the expression in relation to the required type

visitor - an expression visitor

Returns:

the expression after type checking (perhaps augmented with dynamic type checking code)

Throws:

XPathException - if failures occur, for example if the static type of one branch of the conditional is incompatible with the required type

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ContextItemStaticInfo 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)

copy

public Expression copy()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException

Check to ensure that this expression does not contain any 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 updateing subexpression

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

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 class Instruction

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

markTailFunctionCalls

public int markTailFunctionCalls(StructuredQName qName,
                        int arity)

Mark tail-recursive calls on functions. For most expressions, this does nothing.

Overrides:

markTailFunctionCalls in class Expression

Parameters:

qName - the name of the function

arity - the arity (number of parameters) of the function

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.

getItemType

public ItemType getItemType()

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

Overrides:

getItemType in class Instruction

Returns:

the static item type of the instruction

computeCardinality

public int computeCardinality()

Compute the cardinality of the sequence returned by evaluating this instruction

Overrides:

computeCardinality in class Instruction

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 class Instruction

Returns:

a set of flags indicating static properties of this expression

createsNewNodes

public final boolean createsNewNodes()

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

Overrides:

createsNewNodes in class Instruction

Returns:

true if the instruction creates new nodes (or if it can't be proved that it doesn't)

promoteChildren

protected void promoteChildren(PromotionOffer offer)
                        throws XPathException

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

Overrides:

promoteChildren in class Instruction

Parameters:

offer - The type of rewrite being offered

Throws:

XPathException

unordered

public Expression unordered(boolean retainAllNodes,
                   boolean forStreaming)
                     throws XPathException

Replace this expression by a simpler expression that delivers the results without regard to order.

Overrides:

unordered in class Expression

Parameters:

retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.

forStreaming - set to true if optimizing for streaming

Returns:

an expression that delivers the same nodes in a more convenient order

Throws:

XPathException - if the rewrite fails

checkPermittedContents

public void checkPermittedContents(SchemaType parentType,
                          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

Parameters:

parentType - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type

whole - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content

Throws:

XPathException - if the value delivered by this expression cannot be part of the content model of the given type

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                  PathMap.PathMapNodeSet pathMapNodeSet)

Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

Overrides:

addToPathMap in class Expression

Parameters:

pathMap - the PathMap to which the expression should be added

pathMapNodeSet - the set of PathMap nodes to which the paths from this expression should be appended

Returns:

the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

toString

public String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

Overrides:

toString in class Expression

Returns:

a representation of the expression as a string

toShortString

public String toShortString()

Description copied from class: Expression

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class Expression

Returns:

a short string, sufficient to identify the expression

export

public void export(ExpressionPresenter out)

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in class Expression

Parameters:

out - the expression presenter used to display the structure

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.

Specified by:

processLeavingTail in interface TailCallReturner

Specified by:

processLeavingTail in class Instruction

Parameters:

context - the dynamic context of this transformation

Returns:

a TailCall, if the chosen branch ends with a call of call-template or apply-templates. It is the caller's responsibility to execute such a TailCall. If there is no TailCall, returns null.

Throws:

XPathException - if any non-recoverable dynamic error occurs

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 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 relies on the process() method: it "pushes" the results of the instruction to a sequence in memory, and then iterates over this in-memory sequence.

In principle instructions should implement a pipelined iterate() method that avoids the overhead of intermediate storage.

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

iterateEvents

public EventIterator iterateEvents(XPathContext context)
                            throws XPathException

Deliver the result of the expression as a sequence of events.

The events (of class PullEvent) are either complete items, or one of startElement, endElement, startDocument, or endDocument, known as semi-nodes. The stream of events may also include a nested EventIterator. If a start-end pair exists in the sequence, then the events between this pair represent the content of the document or element. The content sequence will have been processed to the extent that any attribute and namespace nodes in the content sequence will have been merged into the startElement event. Namespace fixup will have been performed: that is, unique prefixes will have been allocated to element and attribute nodes, and all namespaces will be declared by means of a namespace node in the startElement event or in an outer startElement forming part of the sequence. However, duplicate namespaces may appear in the sequence.

The content of an element or document may include adjacent or zero-length text nodes, atomic values, and nodes represented as nodes rather than broken down into events.

Overrides:

iterateEvents in class Expression

Parameters:

context - The dynamic evaluation context

Returns:

the result of the expression as an iterator over a sequence of PullEvent objects

Throws:

XPathException - if a dynamic error occurs during expression evaluation

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

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the Choose expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler

getStreamingAdjunct

public ChooseAdjunct getStreamingAdjunct()

Get a class that supports streamed evaluation of this expression

Overrides:

getStreamingAdjunct in class Expression

Returns:

the relevant StreamingAdjunct, or null if none is available