CODEWITHSUNDEEP
prologtransitive-closure
joaquin montero
joaquin montero

Reputation: 9

getting out of local stack at prolog

p(0,0).
p(0,1).
p(0,2).
p(0,3).
p(0,4).
p(1,1).
p(1,2).
p(1,3).
p(1,4).
p(1,0).
p(2,0).
p(2,1).
p(2,2).
p(2,3).
p(2,4).
p(3,0).
p(3,1).
p(3,2).
p(3,3).
p(3,4).
p(4,0).
p(4,1).
p(4,2).
p(4,3).
p(4,4).

adjacent(p(X,Y),p(X,Z)) :-
    p(X,Y),
    p(X,Z),
    Z is Y+1.
adjacent(p(X,Y),p(X,Z)) :-
    p(X,Y),
    p(X,Z),
    Z is Y-1.
adjacent(p(X,Y),p(Z,Y)) :-
    p(X,Y),
    p(X,Z),
    Z is X+1.
adjacent(p(X,Y),p(Z,Y)) :-
    p(X,Y),
    p(X,Z),
    Z is X-1.

adjacentC(X,Y) :-
    adjacent(X,Y).
adjacentC(X,Y) :-
    adjacent(X,Z),
    adjacentC(Z,Y).

I don't know why this code I wrote isn't working.

e.g.:

?- adjacentC((0,0),(4,4)). ERROR

Upvotes: 0

Views: 87

Answers (1)

false
false

Reputation: 10102

Quick answer: The following works and terminates always using closure/3 defined elsewhere.

adjacentD(X,Y) :-
   closure(adjacent,X,Y).

However, this approach is extremely slow, due to the inefficient definition of adjacent/3. Here is a better one / oh forget it, here is a more correct one, first:

adjacent2(p(X0,Y0),p(X,Y)) :-
   p(X0,Y0),
   (  X0 = X,
      p(X,Y),
      abs(Y0-Y) =:= 1
   ;  Y0 = Y,
      p(X,Y),
      abs(X0-X) =:= 1
   ).

Upvotes: 1

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