/* 

  Lazy lists in Picat.

  From Jan Burse 
  https://groups.google.com/forum/#!topic/comp.lang.prolog/vu0_zSd6wdU
  """
  take(0, _, R) :- !, R = [].
  take(N, C, [H|R]) :-
      M is N-1,
      call(C, (H|T)),
      take(M, T, R).

  fib(A, B, (C|fib(B,C))) :-
      C is A+B.

  Credits: This is stripped down modified version of
  Markus Triska prost without using CLP(FD) for elements.
  Here is a sample run:

   Welcome to SWI-Prolog (threaded, 64 bits, version 7.7.1)
   SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.

   ?- take(5,fib(0,1),L).
   L = [1, 2, 3, 5, 8].
 
   ?- take(8,fib(0,1),L).
   L = [1, 2, 3, 5, 8, 13, 21, 34]. 
  """


  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/


import util.
% import cp.


main => go.


go =>
  take(50,$fib(0,1),L),
  writeln(L),
  nl.


take(0, _, R) ?=> 
  R = [].
take(N, C, HR) =>
  HR = [H|R],
  call(C, [H|T]),
  take(N-1, T, R).

fib(A, B, T) =>
   T = $[C|fib(B,C)],
   C = A+B.