[thesz]

As I keep saying, what is a language feature in other languages, is a library in Haskell: https://hackage.haskell.org/package/effect-handlers

And this is how it should be. Not a language feature, but library. Dealing with language feature you deal with compiler and may affect more people than needed, with library you can use (and extend) it as you wish.

[resoluteteeth]

Haskell is probably going to need to get some language features for extensible effects to have acceptable performance (e.g. the unmerged work on eff).