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Truffle SL is an example language implemented using the Truffle API.
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/*
 * Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * The Universal Permissive License (UPL), Version 1.0
 * 
 * Subject to the condition set forth below, permission is hereby granted to any
 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
 * copyright rights in the Software, and any and all patent rights owned or
 * freely licensable by each licensor hereunder covering either (i) the
 * unmodified Software as contributed to or provided by such licensor, or (ii)
 * the Larger Works (as defined below), to deal in both
 * 
 * (a) the Software, and
 * 
 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
 * one is included with the Software each a "Larger Work" to which the Software
 * is contributed by such licensors),
 * 
 * without restriction, including without limitation the rights to copy, create
 * derivative works of, display, perform, and distribute the Software and make,
 * use, sell, offer for sale, import, export, have made, and have sold the
 * Software and the Larger Work(s), and to sublicense the foregoing rights on
 * either these or other terms.
 * 
 * This license is subject to the following condition:
 * 
 * The above copyright notice and either this complete permission notice or at a
 * minimum a reference to the UPL must be included in all copies or substantial
 * portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 * SOFTWARE.
 */
package com.oracle.truffle.sl.nodes.controlflow;

import com.oracle.truffle.api.dsl.*;
import com.oracle.truffle.api.frame.*;
import com.oracle.truffle.api.nodes.*;
import com.oracle.truffle.api.source.*;
import com.oracle.truffle.api.utilities.*;
import com.oracle.truffle.sl.nodes.*;

public final class SLRepeatingNode extends Node implements RepeatingNode {

    /**
     * The condition of the loop. This in a {@link SLExpressionNode} because we require a result
     * value. We do not have a node type that can only return a {@code boolean} value, so
     * {@link #evaluateCondition executing the condition} can lead to a type error.
     */
    @Child private SLExpressionNode conditionNode;

    /** Statement (or {@link SLBlockNode block}) executed as long as the condition is true. */
    @Child private SLStatementNode bodyNode;

    /**
     * Profiling information, collected by the interpreter, capturing whether a {@code continue}
     * statement was used in this loop. This allows the compiler to generate better code for loops
     * without a {@code continue}.
     */
    private final BranchProfile continueTaken = BranchProfile.create();
    private final BranchProfile breakTaken = BranchProfile.create();

    public SLRepeatingNode(SourceSection src, SLExpressionNode conditionNode, SLStatementNode bodyNode) {
        super(src);
        this.conditionNode = conditionNode;
        this.bodyNode = bodyNode;
    }

    public boolean executeRepeating(VirtualFrame frame) {
        if (evaluateCondition(frame)) {
            try {
                /* Execute the loop body. */
                bodyNode.executeVoid(frame);
            } catch (SLContinueException ex) {
                /* In the interpreter, record profiling information that the loop uses continue. */
                continueTaken.enter();
                /* Fall through to next loop iteration. */
            } catch (SLBreakException ex) {
                /* In the interpreter, record profiling information that the loop uses break. */
                breakTaken.enter();
                /* Done executing this loop, exit method to execute statement following the loop. */
                return false;
            }
            return true;
        } else {
            return false;
        }
    }

    private boolean evaluateCondition(VirtualFrame frame) {
        try {
            /*
             * The condition must evaluate to a boolean value, so we call the boolean-specialized
             * execute method.
             */
            return (conditionNode.executeBoolean(frame));
        } catch (UnexpectedResultException ex) {
            /*
             * The condition evaluated to a non-boolean result. This is a type error in the SL
             * program. We report it with the same exception that Truffle DSL generated nodes use to
             * report type errors.
             */
            throw new UnsupportedSpecializationException(this, new Node[]{conditionNode}, ex.getResult());
        }
    }

    @Override
    public String toString() {
        return SLStatementNode.formatSourceSection(this);
    }

}