/* 

  a^nb^nc^n in Picat v3.

  From comp.lang.prolog 2008-01-22.
  Using DCG.

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

*/

import v3_utils.
import cp.

main => go.

% Generate [],abc,aabbcc, ... 
go ?=> 
   anbncn(Ls, []),
   println(Ls),
   % restrict the length
   (Ls.len < 100 -> fail ; true),
   nl.

go => true.

% Using v3_utils.phrase
go2 ?=> 
   phrase(anbncn,Ls),
   println(Ls),
   % restrict the length
   (Ls.len < 100 -> fail ; true),
   nl.

go2 => true.


% From https://stackoverflow.com/questions/28893324/what-does-mean-in-prolog
% Generate N=9 (length: 3*9 = 27)
go3 ?=> 
   start(9,Ls,[]),
   println(Ls),
   println(len=Ls.len),
   fail,
   nl.

go3 => true.


% Get the N of a sequence
go4 ?=> 
   start(N,"aabbcc",[]),
   println(n=N),
   fail,
   nl.

go4 => true.



anbncn --> n_x(N, a), n_x(N, b), n_x(N, c).

n_x(0, _)    --> [].
n_x(s(N), X) --> [X], n_x(N, X).

%Yielding:
%
%   %?- anbncn(Ls, []).
%   %@ Ls = [] ;
%   %@ Ls = [a, b, c] ;
%   %@ Ls = [a, a, b, b, c, c] ;
%   %@ Ls = [a, a, a, b, b, b, c, c, c] a
%   %@ Yes


% From https://stackoverflow.com/questions/28893324/what-does-mean-in-prolog
start(N) --> as(N), bs(N), cs(N).

as(N) --> {N #> 0, M #= N-1}, [a], as(M).
as(0) --> [].

bs(N) --> {N #> 0, M #= N-1}, [b], bs(M).
bs(0) --> [].

cs(N) --> {N #> 0, M #= N-1}, [c], cs(M).
cs(0) --> [].