/*
* Copyright (c) 2007 BUSINESS OBJECTS SOFTWARE LIMITED
* All rights reserved.
*
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* modification, are permitted provided that the following conditions are met:
*
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* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
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* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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/*
* CondTuple.java
* Created: ??
* By: Raymond Cypher
*/
package org.openquark.cal.internal.machine;
import org.openquark.cal.compiler.Expression;
import org.openquark.cal.compiler.QualifiedName;
import org.openquark.cal.module.Cal.Core.CAL_Prelude;
/**
* Expression tuple for conditionals.
*/
public final class CondTuple {
private final Expression kCond; // Condition expr
private final Expression kThen; // Then expr
private final Expression kElse; // Else expr
private CondTuple(Expression kCond, Expression kThen, Expression kElse) {
this.kCond = kCond;
this.kThen = kThen;
this.kElse = kElse;
}
public Expression getConditionExpression () {
return kCond;
}
public Expression getThenExpression () {
return kThen;
}
public Expression getElseExpression () {
return kElse;
}
/**
* Determine if the expression is a conditional (application of "if").
* If the expression matches as an "if" expression, a CondTuple will be populated
* with the condition parameters and returned. Otherwise null returned.
* Creation date: (3/24/00 3:53:55 PM)
* @param e Expression the expression to test
* @return CondTuple instantiated if the expression is an if condition, null otherwise
*/
public static CondTuple isCondOp(Expression e) {
// Look for all the elements of a condition
// Has to match: EAp(EAp(EAp(EVar "if") kCond) kThen) kElse
// Where kCond is the condition expression,
// kThen is the expression to evaluate on kCond being true
// kElse is the expression to evaluate on kCond being false
Expression[] appChain = appChain (e);
if (appChain == null) {
return null;
}
if (appChain.length != 4 || !appChain[0].asVar().getName().equals(QualifiedName.make(CAL_Prelude.MODULE_NAME, "if"))) {
return null;
}
// We have a full match for an if expression
return new CondTuple(appChain[1], appChain[2], appChain[3]);
}
/**
* Convert an application chain to an array.
* @param root
* @return null if this is not an SC application, array of Expression otherwise.
*/
static private Expression[] appChain (Expression root) {
if (root.asAppl() != null) {
// Walk down the left branch.
Expression c = root;
int nArgs = 0;
while (c instanceof Expression.Appl) {
nArgs++;
c = ((Expression.Appl)c).getE1();
}
// At this point c should be an Expression.Var
if (!(c instanceof Expression.Var)) {
return null;
}
Expression[] chain = new Expression [nArgs + 1];
chain[0] = c;
c = root;
for (int i = nArgs; i >= 1; i--) {
chain[i] = ((Expression.Appl)c).getE2();
c = ((Expression.Appl)c).getE1();
}
return chain;
} else
if (root.asTailRecursiveCall() != null) {
return appChain (root.asTailRecursiveCall().getApplForm());
} else
if (root.asVar() != null) {
return new Expression[]{root};
}
return null;
}
}