need help with an argument

[mental00]

Hello all, I need an argument correct(L, X, NL) where L is a list of names, X is a name that exists twice in L and NL is the new list with the name X once.

I wrote this:

correct([], _, _).
correct([H|T], X, NL):-
NL= [H|NL1],
not(member(X, NL)),
correct(T, X, NL1).

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

but it doesnt work, any ideas?

thanks in advance.

 

[kahleen]

First of all, the first clause is incorrect:

correct([], _, _)

On an empty list, no matter what the name is, the result is the empty list, not _

Then:

correct([H|T], X, NL):-
  NL= [H|NL1],
  not(member(X, NL)),
  correct(T, X, NL1).

NL is to be computed. You can't test if X is member in NL while NL is still unbound

A solution to your problem would be:

% empty list
correct([], _, []).

correct([H | T], X, R) :-
    ... what to do if H = X and member(H, T)

correct([H | T], X, [H | R]) :-
    ... what to do if H = X and not(member(H, T))

correct([H | T], X, [H | R]) :-
    ... what to do if H \= X

How about you work on the solution a little and maybe we'll help later on, if you still don't succeed?

 

[mental00]

Thank you for your help.