[erlang-questions] Getting the position of a list item

Igor Ribeiro Sucupira <>
Thu Dec 3 01:58:59 CET 2009


Hum... when you talked about records, I realized I still have one
function that needs to find the position of an item on a list. The
function is used to get the value of a field F on a record, when F is
defined at runtime.

I don't understand exactly what you need, but I guess it's basically
the same thing, isn't it?

On Wed, Dec 2, 2009 at 3:53 PM, Garrett Smith <> wrote:
> On Wed, Dec 2, 2009 at 11:34 AM, Robert Raschke <> wrote:
>> On Wed, Dec 2, 2009 at 5:10 PM, Garrett Smith <> wrote:
>>
>>> I'm missing something basic here :\
>>>
>>> The lists module has keyfind/3 but no find/2, where you want to return
>>> the position of a particular list item. This is surprising.
>>>
>>> Is there a commonly used pattern for this?
>>>
>> Hmm, I fail to come up with a good usage scenario for wanting this. What are
>> you needing the position of an item in a list for?
>
> I'm stitching together record field values and want to get an
> insertion position using a field token.
>
> So, this goes in hard with an "insert_at(Value, N, List_Or_Tuple)"
> type of function.
>
> In general though, there are several functions in the lists module
> that accept a positional argument (N) -- having some easy ways of
> getting N seems reasonable. Functions like l/find and rfind are pretty
> common in the list APIs I'm familiar with.
>
> Garrett
>
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