Prolog: eliminate repetitions in query

Question

I\'ve been trying to write a simple code, that would behave in this manner:

| ?- hasCoppiesOf(X,[a,b,a,b,a,b,a,b]).
X = [a,b] ? ;
X = [a,b,a,b] ? ;
X = [a,b,a,b         


        

Answer 1

I think this is what you're trying for...

coppies(Z,Z,[]).
coppies(X,Z,[Y|Ys]):- \+member(Y,Z),coppies(X,[Y|Z],Ys).
coppies(X,Z,[Y|Ys]):- member(Y,Z),coppies(X,Z,Ys).


copies(M,[Y|Ys]):-coppies(M,[],[Y|Ys]).

Input:

copies(X,[1,2,1,2,1,2]).

Output:

X = [2, 1].

BTW I've used some different names instead..