package client.net.sf.saxon.ce.functions;
import client.net.sf.saxon.ce.expr.*;
import client.net.sf.saxon.ce.om.Item;
import client.net.sf.saxon.ce.om.SequenceIterator;
import client.net.sf.saxon.ce.trans.XPathException;
import client.net.sf.saxon.ce.type.ItemType;
import client.net.sf.saxon.ce.value.BooleanValue;
/**
* Implementation of the fn:exists function
*/
public class Exists extends Aggregate {
public Exists newInstance() {
return new Exists();
}
/**
* Return the negation of the expression
* @return the negation of the expression
*/
public Expression negate() {
FunctionCall fc = SystemFunction.makeSystemFunction("empty", getArguments());
fc.setSourceLocator(getSourceLocator());
return fc;
}
/**
* Perform optimisation of an expression and its subexpressions.
* <p/>
* <p>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.</p>
*
* @param visitor an expression visitor
* @param 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
* {@link client.net.sf.saxon.ce.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws client.net.sf.saxon.ce.trans.XPathException
* if an error is discovered during this phase
* (typically a type error)
*/
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
Expression e2 = super.optimize(visitor, contextItemType);
if (e2 != this) {
return e2;
}
// See if we can deduce the answer from the cardinality
int c = argument[0].getCardinality();
if (c == StaticProperty.ALLOWS_ONE_OR_MORE) {
return new Literal(BooleanValue.TRUE);
} else if (c == StaticProperty.ALLOWS_ZERO) {
return new Literal(BooleanValue.FALSE);
}
// Rewrite
// exists(A|B) => exists(A) or exists(B)
if (argument[0] instanceof VennExpression) {
VennExpression v = (VennExpression)argument[0];
if (v.getOperator() == Token.UNION) {
FunctionCall e0 = SystemFunction.makeSystemFunction("exists", new Expression[]{v.getOperands()[0]});
FunctionCall e1 = SystemFunction.makeSystemFunction("exists", new Expression[]{v.getOperands()[1]});
return new BooleanExpression(e0, Token.OR, e1).optimize(visitor, contextItemType);
}
}
return this;
}
/**
* Evaluate the function
*/
public Item evaluateItem(XPathContext context) throws XPathException {
return BooleanValue.get(effectiveBooleanValue(context));
}
/**
* Evaluate the function in a boolean context
*/
public boolean effectiveBooleanValue(XPathContext c) throws XPathException {
SequenceIterator iter = argument[0].iterate(c);
return iter.next() != null;
}
}
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is “Incompatible With Secondary Licenses”, as defined by the Mozilla Public License, v. 2.0.