Proposed change to libraries

Bjorn Gustavsson <>
Mon Feb 7 12:07:26 CET 2005


Kostis Sagonas <> writes:
[...]
> 
> I.e., change the implementation of map/2 (and similar functions)
> as if defined by:
> 
> map(F, [H|T]) ->
>   [F(H)|map(F, T)];
> map(F, []) when is_function(F) ->	%% andalso is_fun_arity(F) == 1
>   [].

I have some good news and some bad news. :-)

The good news is that we can change lists:map/2 and friends in
R10B-4 to reject an F that is not a fun. That is merely a bug fix
and does not break backward compatibility.

The bad news is that F must be allowed to be a "tuple fun" too,
to keep backward compatibility.

Thus the revised code must look like this:

map(F, [H|T]) ->
  [F(H)|map(F, T)];
map(F, []) when is_function(F) ->	%% andalso is_fun_arity(F) == 1
   [];
map({M,F}, []) when is_atom(M), is_atom(F) ->
   [].

That should still give the Dialyzer more information about the type.

/Björn
-- 
Björn Gustavsson, Erlang/OTP, Ericsson AB



More information about the erlang-questions mailing list