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Truffle SL is an example language implemented using the Truffle API.
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/*
* Copyright (c) 2012, 2020, 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.runtime;
import com.oracle.truffle.api.TruffleLanguage;
import com.oracle.truffle.api.interop.InteropLibrary;
import com.oracle.truffle.api.interop.TruffleObject;
import com.oracle.truffle.api.library.ExportLibrary;
import com.oracle.truffle.api.library.ExportMessage;
import com.oracle.truffle.api.utilities.TriState;
import com.oracle.truffle.sl.SLLanguage;
/**
* The SL type for a {@code null} (i.e., undefined) value. In Truffle, it is generally discouraged
* to use the Java {@code null} value to represent the guest language {@code null} value. It is not
* possible to specialize on Java {@code null} (since you cannot ask it for the Java class), and
* there is always the danger of a spurious {@link NullPointerException}. Representing the guest
* language {@code null} as a singleton, as in {@link #SINGLETON this class}, is the recommended
* practice.
*/
@ExportLibrary(InteropLibrary.class)
@SuppressWarnings("static-method")
public final class SLNull implements TruffleObject {
/**
* The canonical value to represent {@code null} in SL.
*/
public static final SLNull SINGLETON = new SLNull();
private static final int IDENTITY_HASH = System.identityHashCode(SINGLETON);
/**
* Disallow instantiation from outside to ensure that the {@link #SINGLETON} is the only
* instance.
*/
private SLNull() {
}
/**
* This method is, e.g., called when using the {@code null} value in a string concatenation. So
* changing it has an effect on SL programs.
*/
@Override
public String toString() {
return "NULL";
}
@ExportMessage
boolean hasLanguage() {
return true;
}
@ExportMessage
Class extends TruffleLanguage>> getLanguage() {
return SLLanguage.class;
}
/**
* {@link SLNull} values are interpreted as null values by other languages.
*/
@ExportMessage
boolean isNull() {
return true;
}
@ExportMessage
boolean hasMetaObject() {
return true;
}
@ExportMessage
Object getMetaObject() {
return SLType.NULL;
}
@ExportMessage
static TriState isIdenticalOrUndefined(@SuppressWarnings("unused") SLNull receiver, Object other) {
/*
* SLNull values are identical to other SLNull values.
*/
return TriState.valueOf(SLNull.SINGLETON == other);
}
@ExportMessage
static int identityHashCode(@SuppressWarnings("unused") SLNull receiver) {
/*
* We do not use 0, as we want consistency with System.identityHashCode(receiver).
*/
return IDENTITY_HASH;
}
@ExportMessage
Object toDisplayString(@SuppressWarnings("unused") boolean allowSideEffects) {
return "NULL";
}
}
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