Question

Is there a better way to implement Racket’s ormap in Erlang than:

ormap(_, []) -> false;
ormap(Pred, [H|T]) -> 
    case Pred(H) of 
        false -> ormap(Pred, T);
        _ -> {ok, Pred(H)}
    end.

Answer 1

Looks pretty good to me. I’m not sure how smart Erlang is about optimizing these things, but you might want to actually bind the non-false pattern match to a variable, and avoid recomputing Pred(H).

ormap(_, []) -> false;
ormap(Pred, [H|T]) ->
  case Pred(H) of 
    false -> ormap(Pred, T);
    V -> {ok, V}
  end.

The Racket version doesn’t include the ok symbol, but that seems like the Erlangy thing to do so I don’t see anything wrong with it. You might similarly expect Pred to return an attached ok symbol for the non-false case, in which case:

V -> V

or

{ok, V} -> {ok, V}

should work.