[erlang-questions] To name a function

Attila Rajmund Nohl <>
Wed Dec 15 18:13:29 CET 2010


2010/12/15, Ryan Zezeski <>:
> On Wed, Dec 15, 2010 at 11:06 AM, Attila Rajmund Nohl <
> > wrote:
>
>> Hello!
>>
>> I've found at least places in my code where I'd need a function which
>> decides if all, some or none members of a list have a particular
>> property (the list always has at least one element). How to name this
>> function? The code is something like this:
>>
>> f(_F, []) ->
>>  erlang:error({badarg, []});
>>
>> f(F, L) ->
>>  {Has, Not} =
>>    lists:foldr(
>>      fun(E, {H, N}) ->
>>        case f(E) of
>>          true -> {H+1, N};
>>          false -> {H, N+1}
>>        end
>>      end, {0,0}, L),
>>  case {Has, Not} of
>>    {0, _} -> none;
>>    {_, 0} -> all;
>>    _ -> some
>>  end.
>>
>>
> Well, I wouldn't give it any style points but I came up with all_some_none.
>  Also, instead of using fold you could make use of lists:all/2 and
> lists:filter/2.

I could, but that would traverse the list twice (with the length()
guard three times). I don't expect the lists I'm using this function
on to have more than 2000 elements, so on contemporary hardware this
difference is probably not noticeable.


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