Prolog question

Discussion in 'Mac Programming' started by Anteeks, Nov 18, 2012.

  1. macrumors newbie

    Joined:
    Feb 23, 2012
    #1
    I need some help with a prolog question. Almost done with everything, just need help with a small pronlem.

    Question is to make a cooking program. I have some ingredients at home, and some recipes.
    Database has the following information:

    at_home([ingredient(rice,2), ingredient(water,10)]).

    recipe(boiled_rice,[ingredient(rice,4),ingredient(salt,3),ingredient(water,5)]).
    recipe(chicken,[ingredient(chicken,2),ingredient(salt,1),ingredient(pepper,1)]).
    recipe(saltwater,[ingredient(salt,1),ingredient(water,3)]).
    recipe(noodles, [ingredient(noodles,2)|I1]) :- recipe(saltwater,I1).

    Question is:

    Q1: Cook(X); should tell me what I can cook (from the recipes) from the ingredients I have at home.

    Q2: Buy(X, L): should tell me the amount of ingregients I need to buy for dish X.

    My solution:

    at_home([ingredient(rice,2), ingredient(water,10)]).

    recipe(boiled_rice,[ingredient(rice,4),ingredient(salt,3),ingredient(water,5)]).
    recipe(chicken,[ingredient(chicken,2),ingredient(salt,1),ingredient(pepper,1)]).
    recipe(saltwater,[ingredient(salt,1),ingredient(water,3)]).
    recipe(noodles, [ingredient(noodles,2)|I1]) :- recipe(saltwater,I1).

    cook(X) :- at_home(YS), recipe(X,XS), check(XS,YS).

    check([],_).
    check([X|XS],YS) :- enough(X,YS), check(XS,YS).

    enough(ingredient(V,T1),[ingredient(V,T2)|_]) :- T1 =< T2.
    enough(I,[_|YS]) :- enough(I,YS).

    buy(X, L) :- at_home(YS), recipe(X,XS), need(XS, YS, L).

    need([], _, []).
    need([X|XS], YS, L1) :- need(XS, YS, L), tobuy(X, YS, R), ( R = [], L1 = L, ! ; L1 = [R | L]).


    tobuy(ingredient(V,T1), [], ingredient(V, T1)).

    tobuy(ingredient(V, T1), [ingredient(V,T2)|_], R) :-
    !, (T1>T2, L is T1-T2,
    R = ingredient(V, L)
    ;
    R = [])
    .
    tobuy(X, [ingredient(_,_)|TS], R) :- tobuy(X, TS, R).



    Problem:

    Q2 doesn’t work. It gives multiple answers for the same right. Example:

    3 ?- buy(X,L).
    X = boiled_rice,
    L = [ingredient(rice, 2), ingredient(salt, 3)] ;
    X = boiled_rice,
    L = [ingredient(salt, 3)] ;

    If it requires more rice and salt to cook boiled_rice then it shouldn.t at the same time require only more salt.

    What have I done wrong?
     

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