[erlang-questions] list_element()

[Robert Virding]

Your code is basically correct. Some points:

- There is no real benefit in converting to a tuple first as you have
to step over the elements anyway.

- You should seriously consider how/what to return when  you don't
find the element. You return nil. This means that any caller will have
to check return value to see if it was there, which means you may have
to propagate error checking/handling. If it *should* there then maybe
it is best just to signal an error if it not, by just skipping that
clause. If you were putting them in a library then you could have two
functions, one which returns {yes,Index} | no (say) and the other
which just returns index and fails if not found.

- The atom nil has no special significance in Erlang and is seldom used.

Robert


On 27 May 2010 16:31, Henning Diedrich <hd2010@REDACTED> wrote:
> Hi list,
>
> I need to access a list element by index.
>
> I wrote a function but it looks most clumsy.
>
> I am looking for maximal performance. Should I instead convert the list to a
> tuple and use element()?
>
> The lists are ~ 10 to 30 elements in length. (<-- not an attempt to define a
> frame).
>
> For curiosity, does the below tail-recurse correctly?
>
>       listOrd(_, []) -> nil;
>
>       listOrd(Searched, List) when is_list(List) ->
>
>           listOrd(Searched, List, 1).
>
>       listOrd(_, [], _) -> nil;
>
>       listOrd(Searched, [ Element | Tail ], Count) ->
>
>           case Searched == Element of
>               true -> Count;
>               _ -> listOrd(Searched, Tail, Count + 1)
>           end.
>
>
>
> Thanks for your time,
> Henning
>