Take elements from one list and append to other

I want a function that will take two lists A and B and return lists Aout and Bout, such that elements from the beginning of A up to a given element (say the atom 'a') have been removed and appended to the end of B, discarding the character. My attempt below:

% usage: take_while(A, Aout, B, Bout)

take_while([], [], B, B).

take_while(['a'|As], As, B, B).

take_while([A|As], As, B, Bout) :-
        append(B, [A], Bout),
        %take_while(???

The last clause might be the 开发者_如何学编程wrong approach. How do I do this?

Looks like you need to simply add the call to take_while to that last clause: (Actually, I am not sure why the second parameter is needed so I'm removing it from this answer).

   take_while([], [], B, B).

   take_while(['a'|As], As, B, B).

   take_while([A|As], ARem, B, Bout) :-
           append(B, [A], BTemp), take_while(As, ARem, BTemp, Bout).