As suspected, it's not possible to yield mutable values with a closure iterator as it would violate memory safety, similarly to this [github issue](https://github.com/nim-lang/Nim/issues/2361)
The only efficient alternative to my current way is if we could actually chain inline iterators: [https://forum.nim-lang.org/t/2972](https://forum.nim-lang.org/t/2972).
