org.codehaus.groovy.transform.tailrec.InWhileLoopWrapper Maven / Gradle / Ivy

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 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
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 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
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package org.codehaus.groovy.transform.tailrec;

import org.codehaus.groovy.ast.ClassHelper;
import org.codehaus.groovy.ast.MethodNode;
import org.codehaus.groovy.ast.VariableScope;
import org.codehaus.groovy.ast.stmt.BlockStatement;
import org.codehaus.groovy.ast.stmt.ContinueStatement;
import org.codehaus.groovy.ast.stmt.EmptyStatement;
import org.codehaus.groovy.ast.stmt.Statement;
import org.codehaus.groovy.ast.stmt.TryCatchStatement;
import org.codehaus.groovy.ast.stmt.WhileStatement;

import java.util.List;

import static org.codehaus.groovy.ast.tools.GeneralUtils.block;
import static org.codehaus.groovy.ast.tools.GeneralUtils.boolX;
import static org.codehaus.groovy.ast.tools.GeneralUtils.catchS;
import static org.codehaus.groovy.ast.tools.GeneralUtils.constX;
import static org.codehaus.groovy.ast.tools.GeneralUtils.param;
import static org.codehaus.groovy.ast.tools.GeneralUtils.tryCatchS;

/**
 * Wrap the body of a method in a while loop, nested in a try-catch.
 * This is the first step in making a tail recursive method iterative.
 * 
 * There are two ways to invoke the next iteration step:
 * 

 * "continue _RECUR_HERE_" is used by recursive calls outside of closures
 * "throw LOOP_EXCEPTION" is used by recursive calls within closures b/c you cannot invoke "continue" from there
 * 
 */
public class InWhileLoopWrapper {
    public void wrap(MethodNode method) {
        BlockStatement oldBody = (BlockStatement) method.getCode();
        TryCatchStatement tryCatchStatement = tryCatchS(oldBody, EmptyStatement.INSTANCE, catchS(param(ClassHelper.make(GotoRecurHereException.class), "ignore"), new ContinueStatement(InWhileLoopWrapper.LOOP_LABEL)));

        WhileStatement whileLoop = new WhileStatement(boolX(constX(true)), block(new VariableScope(method.getVariableScope()), tryCatchStatement));
        List whileLoopStatements = ((BlockStatement) whileLoop.getLoopBlock()).getStatements();
        if (whileLoopStatements.size() > 0) whileLoopStatements.get(0).setStatementLabel(LOOP_LABEL);
        BlockStatement newBody = block(new VariableScope(method.getVariableScope()));
        newBody.addStatement(whileLoop);
        method.setCode(newBody);
    }

    public static final String LOOP_LABEL = "_RECUR_HERE_";
    public static final GotoRecurHereException LOOP_EXCEPTION = new GotoRecurHereException();
}