net.sf.saxon.functions

Class BooleanFn

public class BooleanFn extends SystemFunction implements Negatable

This class supports the XPath functions boolean(), not(), true(), and false()
Field Summary
static intBOOLEAN
static intFALSE
static intNOT
static intTRUE
Method Summary
voidcheckArguments(ExpressionVisitor visitor)
Static analysis: prevent sorting of the argument
booleaneffectiveBooleanValue(XPathContext c)
Evaluate the effective boolean value
ItemevaluateItem(XPathContext context)
Evaluate the function
booleanisNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable
Expressionnegate()
Create an expression that returns the negation of this expression
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
static ExpressionrewriteEffectiveBooleanValue(Expression exp, ExpressionVisitor visitor, ItemType contextItemType)
Optimize an expression whose effective boolean value is required
Expressionsimplify(ExpressionVisitor visitor)
Simplify the function call.

Field Detail

BOOLEAN

public static final int BOOLEAN

FALSE

public static final int FALSE

NOT

public static final int NOT

TRUE

public static final int TRUE

Method Detail

checkArguments

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

effectiveBooleanValue

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

evaluateItem

public Item evaluateItem(XPathContext context)
Evaluate the function

isNegatable

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

Returns: true if it is

negate

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

Returns: the negated expression

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
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.

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 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)

rewriteEffectiveBooleanValue

public static Expression rewriteEffectiveBooleanValue(Expression exp, ExpressionVisitor visitor, ItemType contextItemType)
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

simplify

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

Parameters: visitor an expression visitor