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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,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.oracle.truffle.sl.nodes.expression;

import java.math.*;

import com.oracle.truffle.api.CompilerDirectives.*;
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.sl.nodes.*;
import com.oracle.truffle.sl.runtime.*;

/**
 * The {@code ==} operator of SL is defined on all types. Therefore, we need a
 * {@link #equal(Object, Object) generic implementation} that can handle all possible types. But
 * since {@code ==} can only return {@code true} when the type of the left and right operand are the
 * same, the specializations already cover all possible cases that can return {@code true} and the
 * generic case is trivial.
 * 
 * Note that we do not need the analogous {@code =!} operator, because we can just
 * {@link SLLogicalNotNode negate} the {@code ==} operator.
 */
@NodeInfo(shortName = "==")
public abstract class SLEqualNode extends SLBinaryNode {

    public SLEqualNode(SourceSection src) {
        super(src);
    }

    @Override
    public abstract boolean executeBoolean(VirtualFrame frame);

    @Specialization
    protected boolean equal(long left, long right) {
        return left == right;
    }

    @Specialization
    @TruffleBoundary
    protected boolean equal(BigInteger left, BigInteger right) {
        return left.equals(right);
    }

    @Specialization
    protected boolean equal(boolean left, boolean right) {
        return left == right;
    }

    @Specialization
    protected boolean equal(String left, String right) {
        return left.equals(right);
    }

    @Specialization
    protected boolean equal(SLFunction left, SLFunction right) {
        /*
         * Our function registry maintains one canonical SLFunction object per function name, so we
         * do not need equals().
         */
        return left == right;
    }

    @Specialization
    protected boolean equal(SLNull left, SLNull right) {
        /* There is only the singleton instance of SLNull, so we do not need equals(). */
        return left == right;
    }

    /**
     * The {@link Fallback} annotation informs the Truffle DSL that this method should be executed
     * when no {@link Specialization specialized method} matches. The operand types must be
     * {@link Object}.
     */
    @Fallback
    protected boolean equal(Object left, Object right) {
        /*
         * We covered all the cases that can return true in specializations. If we compare two
         * values with different types, no specialization matches and we end up here.
         */
        assert !left.equals(right);
        return false;
    }
}