Class Cycle

src/jvm/clojure/lang/Cycle.java:15–107

/* Alex Miller, Dec 5, 2014 */

public class Cycle extends ASeq implements IReduce, IPending {

private static final long serialVersionUID = 4007270937279943908L;

private final ISeq all;      // never null
private final ISeq prev;
private volatile ISeq _current; // lazily realized
private volatile ISeq _next;  // cached

private Cycle(ISeq all, ISeq prev, ISeq current){
    this.all = all;
    this.prev = prev;
    this._current = current;
}

private Cycle(IPersistentMap meta, ISeq all, ISeq prev, ISeq current, ISeq next){
    super(meta);
    this.all = all;
    this.prev = prev;
    this._current = current;
    this._next = next;
}

public static ISeq create(ISeq vals){
    if(vals == null)
        return PersistentList.EMPTY;
    return new Cycle(vals, null, vals);
}

// realization for use of current
private ISeq current() {
    if(_current == null) {
        ISeq current = prev.next();
        _current = (current == null) ? all : current;
    }
    return _current;
}

public boolean isRealized() {
    return _current != null;
}

public Object first(){
    return current().first();
}

public ISeq next(){
    if(_next == null)
        _next = new Cycle(all, current(), null);
    return _next;
}

public Cycle withMeta(IPersistentMap meta){
    if(meta() == meta)
        return this;
    return new Cycle(meta, all, prev, _current, _next);
}