net.sf.saxon.functions
Class BooleanFn

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.FunctionCall
          extended by net.sf.saxon.functions.SystemFunction
              extended by net.sf.saxon.functions.BooleanFn
All Implemented Interfaces:
Serializable, SourceLocator, EvaluableItem, Negatable, SequenceIterable, InstructionInfoProvider

public class BooleanFn
extends SystemFunction
implements Negatable

This class supports the XPath functions boolean(), not(), true(), and false()

See Also:
Serialized Form

Field Summary
static int BOOLEAN
           
static int FALSE
           
static int NOT
           
static int TRUE
           
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
BooleanFn()
           
 
Method Summary
 void checkArguments(ExpressionVisitor visitor)
          Static analysis: prevent sorting of the argument
 boolean effectiveBooleanValue(XPathContext c)
          Evaluate the effective boolean value
 Item evaluateItem(XPathContext context)
          Evaluate the function
 boolean isNegatable(ExpressionVisitor visitor)
          Check whether this specific instance of the expression is negatable
 Expression negate()
          Create an expression that returns the negation of this expression
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
static Expression rewriteEffectiveBooleanValue(Expression exp, ExpressionVisitor visitor, ItemType contextItemType)
          Optimize an expression whose effective boolean value is required
 Expression simplify(ExpressionVisitor visitor)
          Simplify the function call.
 
Methods inherited from class net.sf.saxon.functions.SystemFunction
addDocToPathMap, computeCardinality, computeSpecialProperties, copy, getDetails, getErrorCodeForTypeErrors, getItemType, makeSystemFunction, setDetails
 
Methods inherited from class net.sf.saxon.expr.FunctionCall
addExternalFunctionCallToPathMap, equals, explain, getArguments, getDisplayName, getFunctionName, getNumberOfArguments, hashCode, iterateSubExpressions, preEvaluate, promote, replaceSubExpression, setArguments, setFunctionName, toString, typeCheck
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, evaluateAsString, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

BOOLEAN

public static final int BOOLEAN
See Also:
Constant Field Values

NOT

public static final int NOT
See Also:
Constant Field Values

TRUE

public static final int TRUE
See Also:
Constant Field Values

FALSE

public static final int FALSE
See Also:
Constant Field Values
Constructor Detail

BooleanFn

public BooleanFn()
Method Detail

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
Simplify the function call. Default method is to simplify each of the supplied arguments and evaluate the function if all are now known.

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

checkArguments

public void checkArguments(ExpressionVisitor visitor)
                    throws XPathException
Static analysis: prevent sorting of the argument

Overrides:
checkArguments in class SystemFunction
Parameters:
visitor - the expression visitor
Throws:
XPathException

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
                    throws XPathException
Perform optimisation of an expression and its subexpressions.

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 SystemFunction
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)

isNegatable

public boolean isNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable

Specified by:
isNegatable in interface Negatable
Returns:
true if it is

negate

public Expression negate()
Create an expression that returns the negation of this expression

Specified by:
negate in interface Negatable
Returns:
the negated expression

rewriteEffectiveBooleanValue

public static Expression rewriteEffectiveBooleanValue(Expression exp,
                                                      ExpressionVisitor visitor,
                                                      ItemType contextItemType)
                                               throws XPathException
Optimize an expression whose effective boolean value is required

Parameters:
exp - the expression whose EBV is to be evaluated
visitor - an expression visitor
contextItemType - the type of the context item for this expression
Returns:
an expression that returns the EBV of exp, or null if no optimization was possible
Throws:
XPathException - if static errors are found

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Evaluate the function

Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in class Expression
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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext c)
                              throws XPathException
Evaluate the effective boolean value

Overrides:
effectiveBooleanValue in class Expression
Parameters:
c - The context in which the expression is to be evaluated
Returns:
the effective boolean value
Throws:
XPathException - if any dynamic error occurs evaluating the expression


Copyright (C) Michael H. Kay. All rights reserved.