I'm trying to match a subset of the facts I'm creating, and my testcase was working great!
x([1,2,3,4],'bleah'). x([1,2,4],'bleah2'). x([1,2],'bleah8'). x([1,3,4],'bleah3'). x([5,6,7,8],'bleah5'). x([6,7,8,9],'bleah6'). fuzzy(X,R) :- x(Z, R), subset(X,Z) . remaining(X,Y,D,M) :- x(Z,D) , select(X,Z,N), select(Y,N,M). pair(X,Y,R) :- x([X,Y],R) ; x([Y,X],R). Output: ?- x([1,2|REST],D). REST = [3, 4], D = bleah ; REST = [4], D = bleah2 ; REST = [], D = bleah8 ; false. ?- pair(2,1,D). D = bleah8 ; false. ?- fuzzy([2,1],R). R = bleah ; R = bleah2 ; R = bleah8 ; false. ?- remaining(2,1,D,M). D = bleah, M = [3, 4] ; D = bleah2, M = [4] ; D = bleah8, M = [] ; false.
Then I added a fact to represent my next potential case, and now it's quite broken. I'm new to Prolog, I'm not sure why this is or how to fix it.
x([6,X,8,9],'woot') :- (X+0) > 7. Output: ?- x([1,2|REST],D). REST = [3, 4], D = bleah ; REST = [4], D = bleah2 ; REST = [], D = bleah8 ; false. ?- pair(2,1,D). D = bleah8 ; false. ?- fuzzy([2,1],R). R = bleah ; R = bleah2 ; R = bleah8 ; ERROR: >/2: Arguments are not sufficiently instantiated ^ Exception: (9) _G260+0>7 ? abort % Execution Aborted ?- remaining(2,1,D,M). D = bleah, M = [3, 4] ; D = bleah2, M = [4] ; D = bleah8, M = [] ; ERROR: >/2: Arguments are not sufficiently instantiated ^ Exception: (10) _G270+0>7 ? abort % Execution Aborted ?- x([_,15,_,_],D). D = woot.
Suggestions welcome.
Can X only be a natural number? If yes, then you can change your rule
x([6,X,8,9], 'woot') :- (X+0) > 7.
to
x([6, X, 8, 9], 'woot') :- between(8, inf, X).
This works at least in SWI-Prolog:
?- x(A, B).
A = [6, 8, 8, 9],
B = woot ;
A = [6, 9, 8, 9],
B = woot ;
A = [6, 10, 8, 9],
B = woot ;
...