Prototype for stateful directory traverser

tmp.erl

-module(tmp).
-compile(export_all).

test() ->
    filelib:ensure_dir("level1/level2/level3/"),
    file:write_file("level1/l11", "hello"),
    file:write_file("level1/l12", "hello"),
    file:write_file("level1/l13", "hello"),
    file:write_file("level1/level2/l21", "hello"),
    file:write_file("level1/level2/level3/l31", "hello"),

    State0 = [{dir, "."}],
    State1 = navigate(filename:split("./level1"), State0, "."),
    State2 = navigate(filename:split("./level1/level2"), State1, "."),
    State3 = navigate(filename:split("./level1"), State2, "."),
    State4 = navigate(filename:split("./level1"), State3, "."),
    State5 = navigate(filename:split("./level1"), State4, ".").


loop(Start, In) ->
    case navigate(Start, In, ".") of
        [] ->
            ok;
        Tree ->
            loop(Start, Tree)
    end.

navigate([H|T], Files, Prefix) ->
    case lists:keytake(H, 2, Files) of
        {value, {dir, H, []}, Rest} ->
            Rest;
        {value, {dir, H, Sub}, Rest} ->
            lists:reverse([{dir, H, navigate(T, Sub, filename:join(Prefix, H))} | Rest]);
        {value, {dir, H}, Rest} ->
            lists:reverse([{dir, H, navigate(T, expand(H, Prefix), filename:join(Prefix, H))} | Rest]);
        false ->
            []
    end;
navigate([], Files, Prefix) ->
    iterate(Files, Prefix).

iterate([{dir, Path} | T], Prefix) ->
    iterate([{dir, Path, expand(Path, Prefix)} | T], Prefix);
iterate([{dir, Path, []} | T], Prefix) ->
    iterate(T, Prefix);
iterate([{dir, Path, Files} | T], Prefix) ->
    [{dir, Path, iterate(Files, filename:join([Prefix,Path]))} | T];
iterate([H | T], Prefix) ->
    io:format("~s~n", [filename:join(Prefix, H)]),
    T;
iterate([], Prefix) ->
    [].

expand(Path, Prefix) ->
    Dirname = filename:join([Prefix, Path]),
    {ok, Files0} = file:list_dir(Dirname),
    Files = lists:map(fun(File) ->
                              Filename = filename:join([Dirname, File]),
                              case filelib:is_dir(Filename) of
                                  true ->
                                      {dir, File};
                                  false ->
                                      File
                              end
                      end,
                      Files0),
    lists:reverse(lists:sort(Files)).