A modern programming language that makes developers happier.

kotlinlang

```
list.map {
  if (it.a == key) {
    ...
  } else {
    it
  }
}
```

:man-facepalming: Thanks for pointing out the obvious; I completely forgot about kotlin...

But how would you handle if say, the modification failed with an Optional or an Either, wouldn't it just create a mixed type list that you'd have to re-iterate over to check?

there is `filterMap` for option, and you can in general always use `traverse`. `traverse` is equal to `map` followed by `sequence` and `sequence` can turn a `List&lt;Option&lt;A&gt;&gt;` or `List&lt;Either&lt;L, R&gt;&gt;` into `Option&lt;List&lt;A&gt;&gt;` and `Either&lt;L, List&lt;R&gt;&gt;`. (it short circuits as soon as it finds a None or a Left)

code with traverse:
```
list.traverse(Option.applicative()) {
  if (it.a == key)
    ... (some computation that ends with Option)
  else it.some()
}
```
should produce the same thing

assuming you want to fail the whole computation with Left or None when modification fails

Yes that's what I was after, thanks for your help