Not so Constraint Logic Programming with Mercury

not_so_clp.m

:- module not_so_clp.

:- interface.

:- import_module io.

:- pred main(io::di, io::uo) is det.

:- implementation.

:- import_module int.
:- import_module solutions.

% Demonstrating basic CLP(int)-like solving using non-deterministic search with Mercury.

% A chicken farmer also has some cows for a total of 30 animals, and the animals have 74 legs in all.
% How many chickens does the farmer have?
% https://www.metalevel.at/prolog/optimization
:- pred cow_chicken(int::out, int::out) is nondet.
cow_chicken(Cows, Chickens) :-
  int.nondet_int_in_range(0,30,Chickens),
  int.nondet_int_in_range(0,30,Cows),
  Chickens + Cows = 30,
  Chickens*2 + Cows*4 = 74.

main(!IO) :-
  solutions(pred({A,B}::out) is nondet :- cow_chicken(A, B), CowsChickens),
  io.write(CowsChickens, !IO),
  io.nl(!IO).