/*

  Train example in B-Prolog.

  This is a simple example using table constraint. 
  From SWI prolog manual
  http://www.swi-prolog.org/pldoc/doc_for?object=section%282%2c%20%27A.7%27%2c%20swi%28%27%2fdoc%2fManual%2fclpfd.html%27%29%29
  """
  As another example, consider a train schedule represented as a list
  of quadruples, denoting departure and arrival places and times for each 
  train. In the following program, Ps is a feasible journey of length 
  3 from A to D via trains that are part of the given schedule.
  """

  Answer:
  [[1,2,0,1],[2,3,4,5],[3,4,8,9]]


  Model created by Hakan Kjellerstrand, hakank@gmail.com
  See also my B-Prolog page: http://www.hakank.org/bprolog/

*/


go :-
        threepath(1, 4, Ps,TotalTime),
        writeln(Ps),
        writeln(total_time:TotalTime),nl.

% Valid tuples for the table constraint
trains([(1,2,0,1),(2,3,4,5),(2,3,0,1),(3,4,5,6),(3,4,2,3),(3,4,8,9)]).
 
threepath(A, D, Ps,TotalTime) :-
        Ps = [(A,B,_T0,T1),(B,C,T2,T3),(C,D,T4,_T5)],
        T2 #> T1,
        T4 #> T3,
        trains(Ts),
        % Table constraint
        Ps in Ts,

        TotalTime #= sum([ T :  (_,_,Start,End) in Ps, 
                           [T], T is End-Start]).