net.sf.saxon.instruct
Class Choose

java.lang.Object
  extended bynet.sf.saxon.expr.ComputedExpression
      extended bynet.sf.saxon.instruct.Instruction
          extended bynet.sf.saxon.instruct.Choose
All Implemented Interfaces:
Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

public class Choose
extends Instruction

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

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
Choose(Expression[] conditions, Expression[] actions)
          Construct an xsl:choose instruction
 
Method Summary
 Expression analyze(StaticContext env, ItemType contextItemType)
          Perform static analysis of an expression and its subexpressions.
 void checkPermittedContents(SchemaType parentType, StaticContext env, 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.
 boolean createsNewNodes()
          Determine whether this instruction creates new nodes.
 void display(int level, NamePool pool, java.io.PrintStream out)
          Diagnostic print of expression structure.
 Item evaluateItem(XPathContext context)
          Evaluate an expression as a single item.
 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
 SequenceIterator iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 java.util.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)
 TailCall processLeavingTail(XPathContext context)
          Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.
protected  void promoteInst(PromotionOffer offer)
          Handle promotion offers, that is, non-local tree rewrites.
 Expression simplify(StaticContext env)
          Simplify an expression.
 
Methods inherited from class net.sf.saxon.instruct.Instruction
appendItem, assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, getImplementationMethod, getInstructionInfo, getSourceLocator, isXSLT, process, promote
 
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, markTailFunctionCalls, resetStaticProperties, setLocationId, setParentExpression, typeError, 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 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

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

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
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

analyze

public 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
Specified by:
analyze in class Instruction
Parameters:
env - the static context of the expression
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)

getItemType

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

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

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

iterateSubExpressions

public java.util.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

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

checkPermittedContents

public void checkPermittedContents(SchemaType parentType,
                                   StaticContext env,
                                   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.

Specified by:
checkPermittedContents in interface Expression
Overrides:
checkPermittedContents in class ComputedExpression
Throws:
XPathException

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)
Diagnostic print of expression structure. The expression is written to the System.err output stream

Parameters:
level - indentation level for this expression
out -
pool - NamePool used to expand any names appearing in the expression

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 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.

Specified by:
evaluateItem in interface Expression
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.

Specified by:
iterate in interface Expression
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