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Truffle SL is an example language implemented using the Truffle API.
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 * 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
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 * 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
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 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
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package com.oracle.truffle.sl.nodes.local;

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

/**
 * Node to read a local variable from a function's {@link VirtualFrame frame}. The Truffle frame API
 * allows to store primitive values of all Java primitive types, and Object values. This means that
 * all SL types that are objects are handled by the {@link #readObject} method. When a local
 * variable changes its type, the frame access method throws an {@link FrameSlotTypeException},
 * which causes not rewriting. The rewriting code is generated by the Truffle DSL.
 */
@NodeField(name = "slot", type = FrameSlot.class)
public abstract class SLReadLocalVariableNode extends SLExpressionNode {

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

    /**
     * Returns the descriptor of the accessed local variable. The implementation of this method is
     * created by the Truffle DSL based on the {@link NodeField} annotation on the class.
     */
    protected abstract FrameSlot getSlot();

    @Specialization(rewriteOn = FrameSlotTypeException.class)
    protected long readLong(VirtualFrame frame) throws FrameSlotTypeException {
        return frame.getLong(getSlot());
    }

    @Specialization(rewriteOn = FrameSlotTypeException.class)
    protected boolean readBoolean(VirtualFrame frame) throws FrameSlotTypeException {
        return frame.getBoolean(getSlot());
    }

    @Specialization(rewriteOn = FrameSlotTypeException.class)
    protected Object readObject(VirtualFrame frame) throws FrameSlotTypeException {
        return frame.getObject(getSlot());
    }

    /**
     * This is the generic case that always succeeds. Since we already have another specialization
     * with the same signature above, we need to order them explicitly with the order attribute.
     */
    @Specialization(contains = {"readLong", "readBoolean", "readObject"})
    protected Object read(VirtualFrame frame) {
        return frame.getValue(getSlot());
    }
}