com.saxonica.extra
Class Try

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.FunctionCall
          net.sf.saxon.functions.SystemFunction
              com.saxonica.extra.Try

All Implemented Interfaces:

Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, InstructionInfoProvider

public class Try
extends SystemFunction

This class implements the saxon:try() extension function, which is specially recognized by the system because it uses a non-standard approach to evaluating its arguments

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Try()

Method Summary

int	computeCardinality() Determine the cardinality of the function.
Item	evaluateItem(XPathContext c) Evaluate in a general context
ItemType	getItemType(TypeHierarchy th) Determine the item type of the value returned by the function
SequenceIterator	iterate(XPathContext c) Iterate over the results of the function
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Type-check the expression.
Expression	simplify(StaticContext env) Simplify the function call.
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression.

Methods inherited from class net.sf.saxon.functions.SystemFunction

checkArguments, computeSpecialProperties, display, getDetails, getErrorCodeForTypeErrors, main, makeSystemFunction, setDetails

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

getArguments, getDisplayName, getFunctionNameCode, getNumberOfArguments, iterateSubExpressions, preEvaluate, promote, replaceSubExpression, setArguments, setFunctionNameCode

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getContainingProcedure, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Try

public Try()

Method Detail

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify the function call. Returns the value of the first argument if this is known statically.

Overrides:

simplify in class FunctionCall

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression. This also calls preEvaluate() to evaluate the function if all the arguments are constant; functions that do not require this behavior can override the preEvaluate method.

Overrides:

typeCheck in class FunctionCall

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:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

optimize

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

Type-check the expression. This also calls preEvaluate() to evaluate the function if all the arguments are constant; functions that do not require this behavior can override the preEvaluate method.

Overrides:

optimize in class SystemFunction

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

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 if appropriate to optimize execution

Throws:

StaticError - if an error is discovered during this phase (typically a type error)

XPathException

computeCardinality

public int computeCardinality()

Determine the cardinality of the function.

Overrides:

computeCardinality in class SystemFunction

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the item type of the value returned by the function

Overrides:

getItemType in class SystemFunction

Parameters:

th -

Returns:

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

evaluateItem

public Item evaluateItem(XPathContext c)
                  throws XPathException

Evaluate in a general context

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Expression

Parameters:

c - 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 c)
                         throws XPathException

Iterate over the results of the function

Specified by:

iterate in interface SequenceIterable

Overrides:

iterate in class Expression

Parameters:

c - 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