[erlang-patches] [PATCH] Fix lists:foreach/2's documented spec

Kostis Sagonas <>
Mon Oct 11 15:04:18 CEST 2010


Björn Gustavsson wrote:
> On Sun, Oct 10, 2010 at 7:02 PM, Tuncer Ayaz <> wrote:
>> ---
>>  lib/stdlib/doc/src/lists.xml |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/stdlib/doc/src/lists.xml b/lib/stdlib/doc/src/lists.xml
>> index 92c4eb4..0cf88fe 100644
>> --- a/lib/stdlib/doc/src/lists.xml
>> +++ b/lib/stdlib/doc/src/lists.xml
>> @@ -297,10 +297,10 @@ flatmap(Fun, List1) ->
>>       </desc>
>>     </func>
>>     <func>
>> -      <name>foreach(Fun, List) -> void()</name>
>> +      <name>foreach(Fun, List) -> ok</name>
>>       <fsummary>Apply a function to each element of a list</fsummary>
>>       <type>
>> -        <v>Fun = fun(Elem) -> void()</v>
>> +        <v>Fun = fun(Elem) -> term()</v>
>>         <v> Elem = term()</v>
>>         <v>List = [term()]</v>
>>       </type>
>>
> 
> void() is a convention used in the documentation to mean
> that the function has no useful return value and should be
> ignored. It is used in many places in the documentation.
> Try:
> 
> git grep 'void()' | grep '[.]xml'

Convention or not, the fact remains that a void() type does not exist in 
Erlang. The problem is that even if one is careful enough not to match 
against the result of the lists:foreach/2 call, the return from this 
function can propagate higher up in the function call chain.

   foo1() ->
      ...
      gazonk = foo2(...),        % this one will fail here
      ....

   foo2(...) ->
      ...
      foo3(...).

   ...

   fooN_1(...) ->
      ...
      fooN(...).

   fooN() ->
      ...
      lists:foreach(...).

It would be a much better world if all void() functions were made to 
return some consistent value such as 'ok'.

Kostis


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