A modern programming language that makes developers happier.

kotlinlang

hey anyone got any fancy work arounds kotlin's lack of lower/upper bounds in generics?
I basically want something like
```
sealed abstract class  FingerTree&lt;out A&gt; {
  abstract fun &lt;B &gt;: A&gt; append(a: A): FingerTree&lt;B&gt;
```
where B is a super type of A
I thought this might be a problem someone here has experienced already but can't find anything in the code base.
BTW, this is an arrow related question as hopefully want to submit this as a PR when ready :slightly_smiling_face: