erlang/otp — pull request #102 by seancribbs (2013-10-14 00:43:49+00:00)
Title: Add lists:find/2,3

`lists:find/2,3` returns the first element of the passed list for which the predicate fun returns `true`. If no elements result in the predicate being true, `undefined` (/2) or the given default value (/3) is returned.

## Why this new feature?

A common task is to select the first element from a list that matches a condition, but there is no existing lists function or language feature that avoids traversing the entire list, while still returning a "safe" value. `lists:find/2,3` codifies the pattern of a tail-recursive search for the matching item without resorting to exceptions (used to abort `foreach/2` or `foldl/3`) and always returns either the first matching item, or an otherwise safe value.

## Risks / uncertain artifacts

It is unclear the desired order of arguments for the 3-arity version. I have made the default value the final argument which is consistent with `application:get_env/3` and `proplists:get_value/3`, but most functions in lists place the `List` argument last.

## How did you solve it?

Following the patterns of other functions in the lists module, `lists:find/3` tests the predicate function against the head of the list, returning the head if the predicate passes, or recursing over the tail if it does not.