package net.sf.saxon.expr;
import net.sf.saxon.functions.BooleanFn;
import net.sf.saxon.functions.SystemFunction;
import net.sf.saxon.om.Item;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.BuiltInAtomicType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.BooleanValue;
import net.sf.saxon.instruct.Choose;
import java.util.Iterator;
import java.util.List;
/**
* Boolean expression: two truth values combined using AND or OR.
*/
public class BooleanExpression extends BinaryExpression implements Negatable {
/**
* Construct a boolean expression
* @param p1 the first operand
* @param operator one of {@link Token#AND} or {@link Token#OR}
* @param p2 the second operand
*/
public BooleanExpression(Expression p1, int operator, Expression p2) {
super(p1, operator, p2);
}
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
Expression e = super.typeCheck(visitor, contextItemType);
if (e == this) {
XPathException err0 = TypeChecker.ebvError(operand0, visitor.getConfiguration().getTypeHierarchy());
if (err0 != null) {
err0.setLocator(this);
throw err0;
}
XPathException err1 = TypeChecker.ebvError(operand1, visitor.getConfiguration().getTypeHierarchy());
if (err1 != null) {
err1.setLocator(this);
throw err1;
}
// Precompute the EBV of any constant operand
if (operand0 instanceof Literal && !(((Literal)operand0).getValue() instanceof BooleanValue)) {
operand0 = Literal.makeLiteral(BooleanValue.get(operand0.effectiveBooleanValue(null)));
}
if (operand1 instanceof Literal && !(((Literal)operand1).getValue() instanceof BooleanValue)) {
operand1 = Literal.makeLiteral(BooleanValue.get(operand1.effectiveBooleanValue(null)));
}
}
return e;
}
/**
* Determine the static cardinality. Returns [1..1]
*/
public int computeCardinality() {
return StaticProperty.EXACTLY_ONE;
}
/**
* 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 net.sf.saxon.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException {
final Expression e = super.optimize(visitor, contextItemType);
final TypeHierarchy th = visitor.getConfiguration().getTypeHierarchy();
if (e != this) {
return e;
}
// If the value can be determined from knowledge of one operand, precompute the result
if (operator == Token.AND && (
Literal.isConstantBoolean(operand0, false) || Literal.isConstantBoolean(operand1, false))) {
return new Literal(BooleanValue.FALSE);
}
if (operator == Token.OR && (
Literal.isConstantBoolean(operand0, true) || Literal.isConstantBoolean(operand1, true))) {
return new Literal(BooleanValue.TRUE);
}
// Rewrite (A and B) as (if (A) then B else false()). The benefit of this is that when B is a recursive
// function call, it is treated as a tail call (test qxmp290). To avoid disrupting other optimizations
// of "and" expressions (specifically, where clauses in FLWOR expressions), do this ONLY if B is a user
// function call (we can't tell if it's recursive), and it's not in a loop.
if (e == this && operator == Token.AND &&
operand1 instanceof UserFunctionCall &&
th.isSubType(operand1.getItemType(th), BuiltInAtomicType.BOOLEAN) &&
!visitor.isLoopingSubexpression(null)) {
Expression cond = Choose.makeConditional(operand0, operand1, Literal.makeLiteral(BooleanValue.FALSE));
ExpressionTool.copyLocationInfo(this, cond);
return cond;
}
return this;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
public Expression copy() {
return new BooleanExpression(operand0.copy(), operator, operand1.copy());
}
/**
* Check whether this specific instance of the expression is negatable
*
* @return true if it is
*/
public boolean isNegatable(ExpressionVisitor visitor) {
return true;
}
/**
* Return the negation of this boolean expression, that is, an expression that returns true
* when this expression returns false, and vice versa
*
* @return the negation of this expression
*/
public Expression negate() {
// Apply de Morgan's laws
if (operator == Token.AND) {
// not(A and B) ==> not(A) or not(B)
BooleanFn not0 = (BooleanFn)SystemFunction.makeSystemFunction("not", new Expression[]{operand0});
BooleanFn not1 = (BooleanFn)SystemFunction.makeSystemFunction("not", new Expression[]{operand1});
return new BooleanExpression(not0, Token.OR, not1);
} else {
// not(A or B) => not(A) and not(B)
BooleanFn not0 = (BooleanFn)SystemFunction.makeSystemFunction("not", new Expression[]{operand0});
BooleanFn not1 = (BooleanFn)SystemFunction.makeSystemFunction("not", new Expression[]{operand1});
return new BooleanExpression(not0, Token.AND, not1);
}
}
/**
* Evaluate the expression
*/
public Item evaluateItem(XPathContext context) throws XPathException {
return BooleanValue.get(effectiveBooleanValue(context));
}
/**
* Evaluate as a boolean.
*/
public boolean effectiveBooleanValue(XPathContext c) throws XPathException {
switch(operator) {
case Token.AND:
return operand0.effectiveBooleanValue(c) && operand1.effectiveBooleanValue(c);
case Token.OR:
return operand0.effectiveBooleanValue(c) || operand1.effectiveBooleanValue(c);
default:
throw new UnsupportedOperationException("Unknown operator in boolean expression");
}
}
/**
* Determine the data type of the expression
* @return BuiltInAtomicType.BOOLEAN
* @param th the type hierarchy cache
*/
public ItemType getItemType(TypeHierarchy th) {
return BuiltInAtomicType.BOOLEAN;
}
/**
* Construct a list containing the "anded" subexpressions of an expression:
* if the expression is (A and B and C), this returns (A, B, C).
* @param exp the expression to be decomposed
* @param list the list to which the subexpressions are to be added.
*/
public static void listAndComponents(Expression exp, List list) {
if (exp instanceof BooleanExpression && ((BooleanExpression)exp).getOperator() == Token.AND) {
for (Iterator iter = exp.iterateSubExpressions(); iter.hasNext();) {
listAndComponents((Expression)iter.next(), list);
}
} else {
list.add(exp);
}
// TODO: could do more complete analysis to convert the expression to conjunctive normal form.
// This is done by applying various transformations:
// not(not(X)) => X
// not(P and Q) => not(P) or not(Q)
// not(P or Q) => not(P) and not(Q)
// A or (B and C) => (A or B) and (A or C)
}
}
//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
// you may not use this file except in compliance with the License. You may obtain a copy of the
// License at http://www.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//