/* 

  Difference lists in Picat v3.

  Cf http://hakank.org/picat/difference_lists.pi (Picat v2 version).

  Examples from https://stackoverflow.com/questions/21199436/prolog-difference-list

  Note that one have to $ escape the lists.

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

*/

main => go.


go ?=>
  append_dl($[1,2,3|T]-T, $[4,5,6|W]-W, DL),
  println(t=T),
  println(w=W),
  println(dl=$DL),
  
  nl.

go => true.

% Extracting "plain" lists
go2 ?=>
  append_dl($[1,2,3|T]-T, $[4,5,6|W]-W, $L-[]),
  println(t=T),
  println(w=W),
  println(l=L),
  nl.

go2 => true.

append_dl(A-B, B-C, A-C).