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Truffle SL is an example language implemented using the Truffle API.
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/*
 * Copyright (c) 2012, 2018, 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
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 * Software and the Larger Work(s), and to sublicense the foregoing rights on
 * either these or other terms.
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 * This license is subject to the following condition:
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 * 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
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package com.oracle.truffle.sl.nodes.controlflow;

import com.oracle.truffle.api.frame.VirtualFrame;
import com.oracle.truffle.api.nodes.NodeInfo;
import com.oracle.truffle.api.profiles.BranchProfile;
import com.oracle.truffle.sl.nodes.SLExpressionNode;
import com.oracle.truffle.sl.nodes.SLRootNode;
import com.oracle.truffle.sl.nodes.SLStatementNode;
import com.oracle.truffle.sl.runtime.SLNull;

/**
 * The body of a user-defined SL function. This is the node referenced by a {@link SLRootNode} for
 * user-defined functions. It handles the return value of a function: the {@link SLReturnNode return
 * statement} throws an {@link SLReturnException exception} with the return value. This node catches
 * the exception. If the method ends without an explicit {@code return}, return the
 * {@link SLNull#SINGLETON default null value}.
 */
@NodeInfo(shortName = "body")
public final class SLFunctionBodyNode extends SLExpressionNode {

    /** The body of the function. */
    @Child private SLStatementNode bodyNode;

    /**
     * Profiling information, collected by the interpreter, capturing whether the function had an
     * {@link SLReturnNode explicit return statement}. This allows the compiler to generate better
     * code.
     */
    private final BranchProfile exceptionTaken = BranchProfile.create();
    private final BranchProfile nullTaken = BranchProfile.create();

    public SLFunctionBodyNode(SLStatementNode bodyNode) {
        this.bodyNode = bodyNode;
        addRootTag();
    }

    @Override
    public Object executeGeneric(VirtualFrame frame) {
        try {
            /* Execute the function body. */
            bodyNode.executeVoid(frame);

        } catch (SLReturnException ex) {
            /*
             * In the interpreter, record profiling information that the function has an explicit
             * return.
             */
            exceptionTaken.enter();
            /* The exception transports the actual return value. */
            return ex.getResult();
        }

        /*
         * In the interpreter, record profiling information that the function ends without an
         * explicit return.
         */
        nullTaken.enter();
        /* Return the default null value. */
        return SLNull.SINGLETON;
    }
}