package client.net.sf.saxon.ce.expr;
import client.net.sf.saxon.ce.expr.instruct.Choose;
import client.net.sf.saxon.ce.functions.BooleanFn;
import client.net.sf.saxon.ce.functions.SystemFunction;
import client.net.sf.saxon.ce.om.Item;
import client.net.sf.saxon.ce.trans.XPathException;
import client.net.sf.saxon.ce.type.BuiltInAtomicType;
import client.net.sf.saxon.ce.type.ItemType;
import client.net.sf.saxon.ce.type.TypeHierarchy;
import client.net.sf.saxon.ce.value.BooleanValue;
/**
* Boolean expression: two truth values combined using AND or OR.
*/
public class BooleanExpression extends BinaryExpression {
/**
* 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(getSourceLocator());
throw err0;
}
XPathException err1 = TypeChecker.ebvError(operand1, visitor.getConfiguration().getTypeHierarchy());
if (err1 != null) {
err1.setLocator(getSourceLocator());
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 client.net.sf.saxon.ce.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;
}
Expression op0 = BooleanFn.rewriteEffectiveBooleanValue(operand0, visitor, contextItemType);
if (op0 != null) {
operand0 = op0;
}
Expression op1 = BooleanFn.rewriteEffectiveBooleanValue(operand1, visitor, contextItemType);
if (op1 != null) {
operand1 = op1;
}
// If the value can be determined from knowledge of one operand, precompute the result
if (operator == Token.AND) {
if (Literal.isConstantBoolean(operand0, false) || Literal.isConstantBoolean(operand1, false)) {
// A and false() => false()
// false() and B => false()
return new Literal(BooleanValue.FALSE);
} else if (Literal.isConstantBoolean(operand0, true)) {
// true() and B => B
return forceToBoolean(operand1, th);
} else if (Literal.isConstantBoolean(operand1, true)) {
// A and true() => A
return forceToBoolean(operand0, th);
}
}
if (operator == Token.OR) {
if (Literal.isConstantBoolean(operand0, true) || Literal.isConstantBoolean(operand1, true)) {
// A or true() => true()
// true() or B => true()
return new Literal(BooleanValue.TRUE);
} else if (Literal.isConstantBoolean(operand0, false)) {
// false() or B => B
return forceToBoolean(operand1, th);
} else if (Literal.isConstantBoolean(operand1, false)) {
// A or false() => A
return forceToBoolean(operand0, th);
}
}
// 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;
}
private Expression forceToBoolean(Expression in, TypeHierarchy th) {
if (in.getItemType(th) == BuiltInAtomicType.BOOLEAN && in.getCardinality() == StaticProperty.ALLOWS_ONE) {
return in;
} else {
return SystemFunction.makeSystemFunction("boolean", new Expression[]{in});
}
}
/**
* 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;
}
}
// 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.