Source Code Cross Referenced for BooleanExpression.java in  » XML » saxonb » net » sf » saxon » expr » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » XML » saxonb » net.sf.saxon.expr 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package net.sf.saxon.expr;
002:
003:        import net.sf.saxon.om.Item;
004:        import net.sf.saxon.trans.XPathException;
005:        import net.sf.saxon.type.ItemType;
006:        import net.sf.saxon.type.Type;
007:        import net.sf.saxon.type.TypeHierarchy;
008:        import net.sf.saxon.value.BooleanValue;
009:        import net.sf.saxon.functions.SystemFunction;
010:        import net.sf.saxon.functions.BooleanFn;
011:
012:        import java.util.Iterator;
013:        import java.util.List;
014:
015:        /**
016:         * Boolean expression: two truth values combined using AND or OR.
017:         */
018:
019:        public class BooleanExpression extends BinaryExpression {
020:
021:            public BooleanExpression(Expression p1, int operator, Expression p2) {
022:                super (p1, operator, p2);
023:            }
024:
025:            /**
026:             * Determine the static cardinality. Returns [1..1]
027:             */
028:
029:            public int computeCardinality() {
030:                return StaticProperty.EXACTLY_ONE;
031:            }
032:
033:            /**
034:             * Perform optimisation of an expression and its subexpressions.
035:             * <p/>
036:             * <p>This method is called after all references to functions and variables have been resolved
037:             * to the declaration of the function or variable, and after all type checking has been done.</p>
038:             *
039:             * @param opt             the optimizer in use. This provides access to supporting functions; it also allows
040:             *                        different optimization strategies to be used in different circumstances.
041:             * @param env             the static context of the expression
042:             * @param contextItemType the static type of "." at the point where this expression is invoked.
043:             *                        The parameter is set to null if it is known statically that the context item will be undefined.
044:             *                        If the type of the context item is not known statically, the argument is set to
045:             *                        {@link net.sf.saxon.type.Type#ITEM_TYPE}
046:             * @return the original expression, rewritten if appropriate to optimize execution
047:             * @throws net.sf.saxon.trans.StaticError if an error is discovered during this phase
048:             *                                        (typically a type error)
049:             */
050:
051:            public Expression optimize(Optimizer opt, StaticContext env,
052:                    ItemType contextItemType) throws XPathException {
053:                // Rewrite [A and B] as [if (A) then B else false()]. The benefit of this is that when B is a recursive
054:                // function call, it is treated as a tail call (test qxmp290). To avoid disrupting other optimizations
055:                // of "and" expressions (specifically, where clauses in FLWOR expressions), do this ONLY if B is a user
056:                // function call (we can't tell if it's recursive), and it's not in a loop.
057:                final Expression e = super .optimize(opt, env, contextItemType);
058:                final TypeHierarchy th = env.getNamePool().getTypeHierarchy();
059:                if (e == this 
060:                        && operator == Token.AND
061:                        && operand1 instanceof  UserFunctionCall
062:                        && th.isSubType(operand1.getItemType(th),
063:                                Type.BOOLEAN_TYPE) && !containedInLoop(env)) {
064:                    IfExpression cond = new IfExpression(operand0, operand1,
065:                            BooleanValue.FALSE);
066:                    cond.setParentExpression(getParentExpression());
067:                    return cond;
068:                }
069:                return this ;
070:            }
071:
072:            private boolean containedInLoop(StaticContext env) {
073:                ComputedExpression e = this ;
074:                while (true) {
075:                    Container c = e.getParentExpression();
076:                    if (c instanceof  Expression
077:                            && ExpressionTool.isRepeatedSubexpression(
078:                                    (Expression) c, e, env)) {
079:                        return true;
080:                    } else if (c instanceof  ComputedExpression) {
081:                        e = (ComputedExpression) c;
082:                    } else {
083:                        return false;
084:                    }
085:                }
086:            }
087:
088:            /**
089:             * Return the negation of this boolean expression, that is, an expression that returns true
090:             * when this expression returns false, and vice versa
091:             */
092:
093:            public Expression negate(StaticContext env) {
094:                // Apply de Morgan's laws
095:                if (operator == Token.AND) {
096:                    BooleanFn not0 = (BooleanFn) SystemFunction
097:                            .makeSystemFunction("not", 1, env.getNamePool());
098:                    Expression[] args0 = { operand0 };
099:                    not0.setArguments(args0);
100:                    BooleanFn not1 = (BooleanFn) SystemFunction
101:                            .makeSystemFunction("not", 1, env.getNamePool());
102:                    Expression[] args1 = { operand1 };
103:                    not1.setArguments(args1);
104:                    return new BooleanExpression(not0, Token.OR, not1);
105:                } else {
106:                    BooleanFn not0 = (BooleanFn) SystemFunction
107:                            .makeSystemFunction("not", 1, env.getNamePool());
108:                    Expression[] args0 = { operand0 };
109:                    not0.setArguments(args0);
110:                    BooleanFn not1 = (BooleanFn) SystemFunction
111:                            .makeSystemFunction("not", 1, env.getNamePool());
112:                    Expression[] args1 = { operand1 };
113:                    not1.setArguments(args1);
114:                    return new BooleanExpression(not0, Token.AND, not1);
115:                }
116:            }
117:
118:            /**
119:             * Evaluate the expression
120:             */
121:
122:            public Item evaluateItem(XPathContext context)
123:                    throws XPathException {
124:                return BooleanValue.get(effectiveBooleanValue(context));
125:            }
126:
127:            /**
128:             * Evaluate as a boolean.
129:             */
130:
131:            public boolean effectiveBooleanValue(XPathContext c)
132:                    throws XPathException {
133:                switch (operator) {
134:                case Token.AND:
135:                    return operand0.effectiveBooleanValue(c)
136:                            && operand1.effectiveBooleanValue(c);
137:
138:                case Token.OR:
139:                    return operand0.effectiveBooleanValue(c)
140:                            || operand1.effectiveBooleanValue(c);
141:
142:                default:
143:                    throw new UnsupportedOperationException(
144:                            "Unknown operator in boolean expression");
145:                }
146:            }
147:
148:            /**
149:             * Determine the data type of the expression
150:             * @return Type.BOOLEAN
151:             * @param th
152:             */
153:
154:            public ItemType getItemType(TypeHierarchy th) {
155:                return Type.BOOLEAN_TYPE;
156:            }
157:
158:            /**
159:             * Construct a list containing the "anded" subexpressions of an expression:
160:             * if the expression is (A and B and C), this returns (A, B, C).
161:             * @param exp the expression to be decomposed
162:             * @param list the list to which the subexpressions are to be added.
163:             */
164:
165:            public static void listAndComponents(Expression exp, List list) {
166:                if (exp instanceof  BooleanExpression
167:                        && ((BooleanExpression) exp).getOperator() == Token.AND) {
168:                    for (Iterator iter = exp.iterateSubExpressions(); iter
169:                            .hasNext();) {
170:                        listAndComponents((Expression) iter.next(), list);
171:                    }
172:                } else {
173:                    list.add(exp);
174:                }
175:
176:                // TODO: could do more complete analysis to convert the expression to conjunctive normal form.
177:                // This is done by applying various transformations:
178:                //   not(not(X)) => X
179:                //   not(P and Q) => not(P) or not(Q)
180:                //   not(P or Q) => not(P) and not(Q)
181:                //   A or (B and C) => (A or B) and (A or C)
182:            }
183:        }
184:
185:        //
186:        // The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
187:        // you may not use this file except in compliance with the License. You may obtain a copy of the
188:        // License at http://www.mozilla.org/MPL/
189:        //
190:        // Software distributed under the License is distributed on an "AS IS" basis,
191:        // WITHOUT WARRANTY OF ANY KIND, either express or implied.
192:        // See the License for the specific language governing rights and limitations under the License.
193:        //
194:        // The Original Code is: all this file.
195:        //
196:        // The Initial Developer of the Original Code is Michael H. Kay.
197:        //
198:        // Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
199:        //
200:        // Contributor(s): none.
201:        //
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