/*

  Mr Smith problem in Picat.

  From an IF Prolog example (http://www.ifcomputer.de/)
  """
  The Smith family and their three children want to pay a visit but they
  do not all have the time to do so. Following are few hints who will go
  and who will not:
      o If Mr Smith comes, his wife will come too.
      o At least one of their two sons Matt and John will come.
      o Either Mrs Smith or Tim will come, but not both.
      o Either Tim and John will come, or neither will come.
      o If Matt comes, then John and his father will
        also come.
  """

  The answer should be:
    Mr_Smith_comes      =  0
    Mrs_Smith_comes     =  0
    Matt_comes          =  0
    John_comes          =  1
    Tim_comes           =  1

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

*/

import cp.

main => go.

go =>
   write(findall(L,$mr_smith(L))),nl.

mr_smith(L) =>

   L = [Mr_Smith,Mrs_Smith,Matt, John,Tim],
   L :: 0..1,

   % If Mr Smith comes, his wife will come too.
   Mr_Smith #=> Mrs_Smith,

   % At least one of their two sons Matt and John will come.
   Matt #\/ John,

   % Either Mrs Smith or Tim will come, but not both.
   % Mrs_Smith + Tim #= 1,
   Mrs_Smith #^ Tim,

   % Either Tim and John will come, or neither will come.
   Tim #= John,

   % If Matt comes, then John and his father will also come.
   Matt #=> (John #/\ Mr_Smith),

   solve([],L).