Solving a Logic Puzzle in Prolog

Question

I'm learning Prolog, but I got stuck with this problem and I really don't know how to finish it. I thought that I was right in my code, but I keep getting warnings in Sictus, and I don't know where my mistake is.

Here's the problem:

/*
    File:       fall_dance_competition.pl
    Purpose:    Solve the Fall "Dance Competition" puzzle

    Notes:
    Saturday night, four couples went to the town’s annual fall dance 
    competition. Each couple dressed in matching colors and they all
    performed very well. The competition was fierce but friendly and
    everyone had a grand time. Determine the name of each couple, 
    their place in the competition, and the color each couple wore.

    1. Tom, who wasn’t married to Jean, placed better than Mary 
       and her husband but worse than the West couple did.
    2. The couple wearing brown won the event. Mr. and Mrs. 
       King came in 4th place.
    3. Bill Snow and his wife didn’t wear the green outfits. 
       Jean wasn’t married to John.
    4. The couple wearing blue placed after the couple wearing red 
       but before the King couple.
    5. From 4th place to 1st place, the couples won in the following 
       order: John and his wife, the
       couple wearing blue, Mr. and Mrs. Forest, Brenda and her husband.
    6. George and his wife placed better than Tom and Sara.
*/

And here is my code:

use_module( library(basics)).use_module(library(lists)).

lista([pareja(_,_,_,_,_),pareja(_,_,_,_,_),
       pareja(_,_,_,_,_),pareja(_,_,_,_,_)]).

constraints( S ) :-      
    member(pareja(tom, _, _, _, _), S)
    member(pareja(_, jean, _, _, _), S)
    member(pareja(_, mary, _, _, _), S)
    member(pareja(_, _, west, _, _), S)
    perm2(Left_1, Right_1, pareja(tom, _, _, _, _), pareja(_, mary, _, _, _))
    nextto(Left_1, Right_1, S)
    perm2(Left_2, Right_2, pareja(_, _, west, _, _), pareja(tom, _, _, _, _))
    nextto(Left_2, Right_2, S)
    S = [pareja(_, _, _, 1, brown), _, _, _]
    S = [_, _, _, pareja(_, _, king, 4, _)]
    member(pareja(bill, _, snow, _, _), S)
    member(pareja(_, _, _, _, green), S)
    member(pareja(john, _, _, _, _), S)
    nextto(pareja(_, _, _, _, red), pareja(_, _, _, _, blue), S)
    nextto(pareja(_, _, _, _, blue), pareja(_, _, king, _, _), S)
    S = [_, _, _, pareja(john, _, _, 4, _)]
    S = [_, _, pareja(_, _, _, 3, blue), _]
    S = [_, pareja(_, _, forest, 2, _), _, _]
    S = [pareja(_, brenda, _, 1, _), _, _, _]   
    member(pareja(george, _, _, _, _), S)
    member(pareja(tom, sara, _, _, _), S)
    nextto(pareja(george, _, _, _, _), pareja(tom, sara, _, _, _), S).

green( Who ) :-
    lista(S),
    constraints(S),
    member(pareja(_, Who, _, _, green), S). 

nextto(X, Y, List) :- append(_, [X,Y|_], List).

append([X|Y],Z,[X|W]) :- append(Y,Z,W).  
append([],X,X).

member(X,[X|T]).
member(X,[H|T]) :- member(X,T).

perm2(X,Y, X,Y).
perm2(X,Y, Y,X).

I used some examples of the Zebra puzzle to do it.

you forgot the commas ! member(pareja(tom, _, _, _, _), S) , etc etc — CapelliC

Paulo Moura Paulo Moura · Accepted Answer · 2013-10-21T21:54:01

Change the first line of your program to:

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

Check if that solves the problem. use_module/1 is a directive and must be written as such.

Solving a Logic Puzzle in Prolog

2 Answers