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

Garrett Smith <>
Wed Dec 2 18:53:43 CET 2009


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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