LazyList.java

// ex: se sts=4 sw=4 expandtab:

/*
 * Yeti core library.
 *
 * Copyright (c) 2007,2008 Madis Janson
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package yeti.lang;

/** Yeti core library - Lazy list. */
public final class LazyList extends LList {
    private Fun promise;
    private AList rest;

    public LazyList(Object first, Fun rest) {
        super(first, null);
        promise = rest;
    }

    public synchronized AList rest() {
        if (promise != null) {
            rest = (AList) promise.apply(null);
            promise = null;
        }
        return rest;
    }

    public String toString() {
        StringBuffer buf = new StringBuffer("[");
        buf.append(Core.show(first()));
        AIter i = rest();
        for (int n = 0; i != null && ++n <= 100; i = i.next()) {
            buf.append(',');
            buf.append(Core.show(i.first()));
        }
        if (i != null) {
            buf.append("...");
        }
        buf.append(']');
        return buf.toString();
    }
}