haskell prelude

[Olexandr Demura]

that library written with haskell laziness in mind which is not present in java.
you can add additional laziness by replacing `fibs.eval(y, z + y)`
with Iterable `() -> fibs.eval(y, z + y).iterator()`,
but that would not help, since `cons` requests iterator immediately,
causing the same problem.
so you need one more additional layer - lazy Iterator.
but Iterator is not a SAM, so it can't be named elegant:
final private static Function2<Integer, Integer, Iterable<Integer>> fibs
  = (z, y) -> cons(z, cons(y, () -> new Iterator<Integer>() {
    Iterator<Integer> delegate;
    Iterator<Integer> getDelegate() {
      if (delegate == null) delegate = fibs.eval(y, z + y).iterator();
      return delegate;
    }
    public boolean hasNext() { return true; }
    public Integer next() { return getDelegate().next(); }
  }));
IMO it is not any better that plain old
final private static Function2<Integer, Integer, Iterable<Integer>> fibs
  = (z, y) -> (() -> new Iterator<Integer> {
    int curr = z;
    int next = y;
    public boolean hasNext() { return true; }
    public Integer next() {
      int r = curr;
      curr = next;
      next = r + curr;
      return r;
    }
  });

> Date: Thu, 21 Jun 2012 15:33:10 +0200
> From: Luc Duponcheel <luc.duponcheel at gmail.com>
> Subject: haskell prelude
> To: lambda-dev at openjdk.java.net
> Message-ID:
>        <CADO5TNtNy+4Td1cXvVVV-kysVhsp2LZzcj1wxEKUQb0QNAWp2w at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Some time ago Sven Eric Panitz posted an experimental haskell prelude
> library to this group (one of his goals being to work with "infinite
> iterables" (right?))
>
>
> So I tried out something similar to
>
> public class Test{
>  final private static Function2<Integer, Integer, Iterable<Integer>> fibs =
>    (Integer z, Integer y) -> cons(z, cons(y, fibs.eval(y, z + y)));
>  public static void main(String[] args){
>    System.out.println(take(5, fibs.eval(1, 1)));
>  }
> }
>
> but this results in a stack overflow
>
> So my question to Sven (and others (?)) is:
> is there an elegant similar way to define fibs without this issue?
>
>
> thx
>
> Luc
>
> --
>   __~O
>  -\ <,
> (*)/ (*)
>
> reality goes far beyond imagination