Comments on: String concatenation

By: trung

trung — Thu, 16 Jul 2009 14:48:31 +0000

Thanks Denny for the comment.
Hmm, I though initially that ++ is quite native, why they used it in lists:concat/1 implementation then?

By: Denny Abraham

Denny Abraham — Thu, 16 Jul 2009 02:57:36 +0000

Hi Trung,

According to Programming Erlang, the source for the lists module is only an illustrative implementation. Use of ++ is discouraged for all but trivially small lists.

-Denny

By: trung

trung — Sun, 10 May 2009 15:15:00 +0000

Thanks, Fabian.
I’ve looked at the source code for lists.erl, your’re right, lists:concat/1 uses ++ for concatenation:

concat(List) ->
flatmap(fun thing_to_list/1, List).

thing_to_list(X) when is_integer(X) -> integer_to_list(X);
thing_to_list(X) when is_float(X) -> float_to_list(X);
thing_to_list(X) when is_atom(X) -> atom_to_list(X);
thing_to_list(X) when is_list(X) -> X. %Assumed to be a string

flatmap(F, [Hd|Tail]) ->
F(Hd) ++ flatmap(F, Tail);

By: Fabian Alenius

Fabian Alenius — Fri, 08 May 2009 15:09:02 +0000

Ops, I’m blind. Seems you already have an example of ++.

By: Fabian Alenius

Fabian Alenius — Fri, 08 May 2009 15:03:42 +0000

You could also do X ++ Y, I’m not sure if it’s just syntactic sugar for lists:concat(…) or not but I suspect it might be.