/*

  Smuggler's knapsack problem in SICStus Prolog.

  Marriott & Stucker: 'Programming with constraints', page  101f, 115f

  Smuggler's knapsack.
  
  A smuggler has a knapsack with a capacity of 9 units.
              Unit       Profit
  Whisky:     4 units    15 dollars
  Perfume:    3 units    10 dollars
  Cigarettes: 2 units     7 dollars

  What is the optimal choice?

  Compare with the following model:
  * ECLiPSe: http://www.hakank.org/eclipse/smuggler_knapsack.ecl


  Model created by Hakan Kjellerstrand, hakank@bonetmail.com
  See also my SICStus Prolog page: http://www.hakank.org/sicstus/

*/

:-use_module(library(clpfd)).
:-use_module(library(lists)).

go:-
        findall([W,P,C,Profit,Constraint],smuggler([W,P,C,Profit,Constraint],9),L),
        write(L),nl.

go2:-
        List = [2,3,5,7,11,13,17,23,29,31],
        ( foreach(L, List)
        do
          smuggler(X,L),
          write(X),nl
        ).



smuggler([W,P,C,Profit,Constraint],Constraint) :-

        domain([W,P,C], 0,9),

        %                 Unit       Profit
        % Whisky:     4 units    15 dollars
        % Perfume:    3 units    10 dollars
        % Cigarettes: 2 units     7 dollars

        % Units
        4*W  + 3*P  + 2*C #=< Constraint,

        % Profit.
        15*W + 10*P + 7*C #= Profit,

        NegProfit #= Profit * (-1),
        
        labeling([minimize(NegProfit)], [W,P,C,Profit,Constraint]).