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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// 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.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr;
import net.sf.saxon.expr.instruct.Choose;
import net.sf.saxon.expr.parser.*;
import net.sf.saxon.functions.SystemFunction;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.BuiltInAtomicType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.BooleanValue;
import java.util.Collection;
public class AndExpression extends BooleanExpression {
/**
* Construct a boolean AND expression
*
* @param p1 the first operand
* @param p2 the second operand
*/
public AndExpression(Expression p1, Expression p2) {
super(p1, Token.AND, p2);
}
@Override
protected Expression preEvaluate() {
// If the value can be determined from knowledge of one operand, precompute the result
if (Literal.isConstantBoolean(getLhsExpression(), false) || Literal.isConstantBoolean(getRhsExpression(), false)) {
// A and false() => false()
// false() and B => false()
return Literal.makeLiteral(BooleanValue.FALSE, this);
} else if (Literal.hasEffectiveBooleanValue(getLhsExpression(), true)) {
// true() and B => B
return forceToBoolean(getRhsExpression());
} else if (Literal.hasEffectiveBooleanValue(getRhsExpression(), true)) {
// A and true() => A
return forceToBoolean(getLhsExpression());
} else {
return this;
}
}
/**
* 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.
*
* @param visitor an expression visitor
* @param contextInfo 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)
*/
/*@NotNull*/
@Override
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException {
Expression t = super.optimize(visitor, contextInfo);
if (t != this) {
return t;
}
// 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.
TypeHierarchy th = visitor.getConfiguration().getTypeHierarchy();
if ( getRhsExpression() instanceof UserFunctionCall &&
th.isSubType(getRhsExpression().getItemType(), BuiltInAtomicType.BOOLEAN) &&
!ExpressionTool.isLoopingSubexpression(this, null)) {
Expression cond = Choose.makeConditional(
getLhsExpression(), getRhsExpression(), Literal.makeLiteral(BooleanValue.FALSE, this));
ExpressionTool.copyLocationInfo(this, cond);
return cond;
}
return this;
}
@Override
public double getCost() {
// Assume the RHS will be evaluated 50% of the time
return getLhsExpression().getCost() + getRhsExpression().getCost() / 2;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
* @param rebindings variables that need to be rebound
*/
/*@NotNull*/
@Override
public Expression copy(RebindingMap rebindings) {
AndExpression a2 = new AndExpression(getLhsExpression().copy(rebindings), getRhsExpression().copy(rebindings));
ExpressionTool.copyLocationInfo(this, a2);
return a2;
}
/**
* 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
*/
@Override
public Expression negate() {
// Apply de Morgan's laws
// not(A and B) ==> not(A) or not(B)
Expression not0 = SystemFunction.makeCall("not", getRetainedStaticContext(), getLhsExpression());
Expression not1 = SystemFunction.makeCall("not", getRetainedStaticContext(), getRhsExpression());
return new OrExpression(not0, not1);
}
/**
* Get the element name used to identify this expression in exported expression format
*
* @return the element name used to identify this expression
*/
@Override
protected String tag() {
return "and";
}
/**
* Evaluate as a boolean.
*/
@Override
public boolean effectiveBooleanValue(XPathContext c) throws XPathException {
return getLhsExpression().effectiveBooleanValue(c) && getRhsExpression().effectiveBooleanValue(c);
}
/**
* Generate an 'and' tree over a set of expressions
* @param exprs the expressions to be "and'ed" together
* @return the root of the new expression tree
*/
public static Expression distribute(Collection exprs) {
Expression result = null;
if(exprs != null) {
boolean first = true;
for(Expression e: exprs) {
if(first){
first = false;
result = e;
} else {
result = new AndExpression(result,e);
}
}
}
return result;
}
}