:- op(700, xfx, l).
:- op(700, xfx, r).

From l To :- From to To-_.
From r To :- From to _-To.

answer(Answer) :- path([], aaa, Path), length(Path, Answer).

path(_, zzz, []) :- !.  % getting full path instead of just length for debugging
path(Directions, From, [Move | Cdr]) :-
    next_step(Directions, Move, Remain),
    G =.. [Move, From, To], G,
    path(Remain, To, Cdr).

next_step([Move | Remain], Move, Remain).
next_step([], Move, Remain) :- direction(Str), atom_chars(Str, [Move | Remain]).