net.sf.saxon.instruct

Class Choose

public class Choose extends Instruction

Compiled representation of an xsl:choose or xsl:if element in the stylesheet. Also used for typeswitch in XQuery.
Constructor Summary
Choose(Expression[] conditions, Expression[] actions)
Construct an xsl:choose instruction
Method Summary
voidcheckPermittedContents(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.
booleancreatesNewNodes()
Determine whether this instruction creates new nodes.
voiddisplay(int level, NamePool pool, PrintStream out)
Diagnostic print of expression structure.
ItemevaluateItem(XPathContext context)
Evaluate an expression as a single item.
intgetImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
intgetInstructionNameCode()
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.
ItemTypegetItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instruction
SequenceIteratoriterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence.
IteratoriterateSubExpressions()
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)
booleanmarkTailFunctionCalls()
Mark tail calls on used-defined functions.
Expressionoptimize(Optimizer opt, StaticContext env, ItemType contextItemType)
TailCallprocessLeavingTail(XPathContext context)
Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.
protected voidpromoteInst(PromotionOffer offer)
Handle promotion offers, that is, non-local tree rewrites.
Expressionsimplify(StaticContext env)
Simplify an expression.
ExpressiontypeCheck(StaticContext env, ItemType contextItemType)

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

checkPermittedContents

public 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. 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.

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).

display

public void display(int level, NamePool pool, 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

evaluateItem

public Item evaluateItem(XPathContext context)
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.

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.

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.

getItemType

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

Parameters: th

Returns: the static item type of the instruction

iterate

public SequenceIterator iterate(XPathContext context)
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.

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 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)

markTailFunctionCalls

public boolean markTailFunctionCalls()
Mark tail calls on used-defined functions. For most expressions, this does nothing.

optimize

public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType)

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.

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

promoteInst

protected void promoteInst(PromotionOffer offer)
Handle promotion offers, that is, non-local tree rewrites.

Parameters: offer The type of rewrite being offered

Throws: XPathException

simplify

public Expression simplify(StaticContext env)
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).

Returns: the simplified expression

Throws: XPathException if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(StaticContext env, ItemType contextItemType)