Join a list of elements in Erlang, adding a separator between them

lists_join.erl

%% @doc Join a a list of elements adding a separator between
%%      each of them.
-spec join(iolist(), Sep :: term()) -> iolist().
join([Head | Tail], Sep) ->
    join_list_sep(Tail, Sep, [Head]);
join([], _Sep) ->
    [].

-spec join_list_sep(iolist(), Sep :: term(), Acc :: iolist()) -> iolist().
join_list_sep([Head | Tail], Sep, Acc) ->
    join_list_sep(Tail, Sep, [Head, Sep | Acc]);
join_list_sep([], _Sep, Acc) ->
    lists:reverse(Acc).