hanoi.erl

-module(hanoi).
-compile(export_all).

hanoi(N) ->
    hanoi(N, a, c, [], fun lists:reverse/1).

hanoi(0, _, _, Moves, K) ->
    K(Moves);
hanoi(N, From, To, Moves, K) ->
    [Temp] = [a,b,c] -- [From, To],
    hanoi(N-1, From, Temp, Moves,
          fun(Moves) ->
                  hanoi(N-1, Temp, To, [{N, From, To}|Moves], K)
          end).

print_moves([]) ->
    done;
print_moves([{N, From, To}|Moves]) ->
    io:format("move disk ~w from ~w to ~w~n", [N, From, To]),
    print_moves(Moves).

main([N]) ->
    print_moves(hanoi(list_to_integer(atom_to_list(N)))).

%%
% Example:
%  $ erl -noshell -s hanoi main 3 -s init stop
%  move disk 1 from a to c
%  move disk 2 from a to b
%  move disk 1 from c to b
%  move disk 3 from a to c
%  move disk 1 from b to a
%  move disk 2 from b to c
%  move disk 1 from a to c
%  $