Erlang's binary:join/1

gistfile1.erl

join([], _) -> []; %% or should it be <<"">> for a consistency sake?
join([H|[]], _) -> H;
join(List, Sep) when is_list(Sep)  ->
  join(List, list_to_binary(Sep));
join([H|T], Sep) ->
  join(T, H, Sep).

join([], Acc, _) ->
  Acc;
join([H|T], Acc, Sep) ->
  join(T, <<Acc/binary, Sep/binary, H/binary>>, Sep).

-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").

join_test_() ->
  List = [<<"a">>, <<"b">>, <<"c">>],
  [
    ?_assertEqual(join(List, ", "), <<"a, b, c">>),
    ?_assertEqual(join(List, <<"|">>), <<"a|b|c">>),
    ?_assertEqual(join([<<"a">>], ", "), <<"a">>),
    ?_assertEqual(join([], ", "), [])
  ].

-endif.