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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Annie Wang
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

package com.google.javascript.rhino;

import com.google.javascript.jscomp.base.Tri;

/**
 * An enum for representing truthiness and nullishness of outcomes. The values are TRUE, FALSE,
 * FALSE_NOT_NULL, and NULLISH. FALSE represents all falsy values so it contains both FALSE_NOT_NULL
 * and NULLISH. It specifically differentiates between falsy and explicitly nullish values. e.g. 0
 * is falsy but not nullish.
 */
public enum Outcome {
  /** Represents truthy values. For example: {}, true, 1, etc. */
  TRUE {
    @Override
    public boolean isTruthy() {
      return true;
    }

    @Override
    public Tri isNullish() {
      return Tri.FALSE;
    }

    @Override
    public Outcome not() {
      return Outcome.FALSE;
    }
  },

  /** Represents falsy values. For examples: '', 0, false, null, etc. */
  FALSE {
    @Override
    public boolean isTruthy() {
      return false;
    }

    @Override
    public Tri isNullish() {
      return Tri.UNKNOWN;
    }

    @Override
    public Outcome not() {
      return Outcome.TRUE;
    }
  },

  FALSE_NOT_NULL {
    @Override
    public boolean isTruthy() {
      return false;
    }

    @Override
    public Tri isNullish() {
      return Tri.FALSE;
    }

    @Override
    public Outcome not() {
      return Outcome.TRUE;
    }
  },

  NULLISH {
    @Override
    public boolean isTruthy() {
      return false;
    }

    @Override
    public Tri isNullish() {
      return Tri.TRUE;
    }

    @Override
    public Outcome not() {
      return Outcome.TRUE;
    }
  };

  /** Determines whether an Outcome enum value is truthy. */
  public abstract boolean isTruthy();

  /**
   * Determines whether an Outcome enum value is nullish. Using Tri instead of a boolean because 0
   * is Outcome.FALSE but not nullish so sometimes it is unclear.
   */
  public abstract Tri isNullish();

  /** Gets the {@code not} of {@code this}. */
  public abstract Outcome not();

  /** Gets the Outcome for the given boolean. */
  public static Outcome forBoolean(boolean val) {
    return val ? Outcome.TRUE : Outcome.FALSE;
  }
}