IterableSeq.java

/*
 * Vitry, copyright (C) Hans Hoglund 2011
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * at your option) any later version.
 * 
 * This program 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 General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * See COPYING.txt for details.
 */
package vitry.runtime.struct;

import java.util.Iterator;


/**
 * Sequence adapted from an Iterable. Fetches a single iterator from the given
 * object at construction time and traverses it as required.
 * 
 * Mutating the iterable is not recommended.
 * 
 * TODO 
 *      Synchronization? 
 *          Make eager variant that advances headed/tailed state upon
 *          construction?
 *  
 */
public class IterableSeq<T> extends AbstractSeq<T>
{
    private Iterable<T> itbl; // Store for iterator in the leading node
    private Iterator<T> it;
    private T head;
    private Seq<T> tail;
    private boolean headed = false;
    private boolean tailed = false;

    public IterableSeq(Iterable<T> itbl) {
        this.itbl = itbl;
        this.it = itbl.iterator();
    }

    private IterableSeq(Iterable<T> itbl, Iterator<T> it) {
        this.itbl = itbl;
        this.it = it;
    }

    public Iterator<T> iterator()
    {
        return itbl != null ? itbl.iterator() : super.iterator();
    }

    public T head()
    {
        if (!headed)
        {
            head = it.next();
            headed = true;
        }
        return head;
    }

    public Seq<T> tail()
    {
        if (!tailed)
        {
            head();
            if (it.hasNext())
                tail = new IterableSeq<T>(null, it);
            tailed = true;
        }
        return tail;
    }

    public boolean hasTail()
    {
        if (!tailed)
            tail();
        return !Seqs.isNil(tail);
    }
}