@groovy.transform.TypeChecked
 
class Unfoldr<A,B> implements java.util.Iterator<A>
{
  public Unfoldr(Closure<Object[]> f, B init) 
  {
    this.f = f;
    this.state = f(init);
  }
 
  public synchronized A next() throws java.util.NoSuchElementException
  {
    if (hasNext())
    {
      A curr = state[0];
      state = f(state[1]);
      return curr;
    }
    else
    {
      throw new java.util.NoSuchElementException();
    }
  }
 
  public synchronized boolean hasNext() 
  {
    return state != null;
  }
 
  public void remove() { throw UnsupportedOperationException; }
 
  private Closure<Object[]> f;
 
  private Object[] state;
}
 
def currify(fn) {
    { Object... args ->
        if (args.size() == fn.maximumNumberOfParameters) {
            fn(*args)
        } else {
            currify(fn.curry(*args))
        }
    }
};
 
def unfoldr = currify { f, init -> new Unfoldr(f, init) };
 
def map = currify { f, l -> unfoldr({ l2 -> if (l2.hasNext()) { def e = l2.next(); return [f(e), l2]} else { return null; } } , l.iterator())}
 
def splitlist = currify {
n, l ->
  unfoldr(
    { 
      l2 -> 
        try 
        { 
          def a = new Object[n];
          for (i in 0..(n-1))
          {
            a[i] = l2.next();
          }
          return [a, l2]; 
        } 
        catch (java.util.NoSuchElementException e) 
        {
          return null;
        }
    }, 
    l
  )
};
 
Iterator.metaClass.rightShift = { PrintStream os -> delegate.each({ x -> os.println(x) }) }
Iterator.metaClass.rightShift = { Closure f -> f(delegate) }
 
id = { x -> x }
f = currify { x -> x }
 
println "A: "
[[1,2],[3,4]].iterator() >> System.out
println "B: "
[1,2,3,4].iterator() >> splitlist(2) >> System.out
println "C: "
[[1,2],[3,4]].iterator() >> map(id) >> System.out
println "D: "
[1,2,3,4].iterator() >> splitlist(2) >> map(id) >> System.out
println "E: "
[[1,2],[3,4]].iterator() >> map(f) >> System.out
println "F: "
[1,2,3,4].iterator() >> splitlist(2) >> map(f) >> System.out
 

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