/*
 * Either.java
 * Copyright (C) 2004-2005, Bjorn Bringert (bringert@cs.chalmers.se)
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package se.chalmers.cs.gf.util;

import java.util.NoSuchElementException;

/**
 *  A simple variant type.
 */
public class Either<A,B> {

        private A left;
        private B right;
        private boolean isLeft;
        
        private Either(A left, B right, boolean isLeft) {
                this.left = left;
                this.right = right;
                this.isLeft = isLeft;
        }

        public boolean isLeft() {
                return isLeft;
        }

        public A getLeft() {
                if (!isLeft)
                        throw new NoSuchElementException("Called getLeft() when there is only a right.");
                return left;
        }

        public B getRight() {
                if (isLeft)
                        throw new NoSuchElementException("Called getRight() when there is only a left.");
                return right;
        }

        public static <A,B> Either<A,B> mkLeft (A x) {
                return new Either<A,B>(x, null, true);
        }

        public static <A,B> Either<A,B> mkRight (B x) {
                return new Either<A,B>(null, x, false);
        }

}