Jeffrey Young

> On second thought, I think that this printing thing is a bug. It prints the argument name because of this line: This is not a bug. A closure is...

alright I've fixed the names, now more tests and cleanup and this should be good to go

Basically done, I want to do another pass over the code then squash

- [x] make error messages consistent - [x] add a less primitive debugger, one that automatically grabs the `currentPhase` and constructs the `ExpansionErr` given an `ErrorKind`.

I'm in agreement with @noughtmare and @tomjaguarpaw for both `dup` and `arr2` in `Control.Arrow`

> do you think we should merge the PRs whose CI currently fail but are verified working before moving to the new repo? I think we should just remake them...

cc @bgamari @MangoIV I've opened https://gitlab.haskell.org/ghc/ghc.nix/-/merge_requests/6 which migrates #188 #189 #190

@gelisam is there anything holding this up? It seems like a straightforward refactor

I am in favor of this change. Separating the derived `mappend` for `Monoid a` from the `mappend` for `Monoid (Generically a)` to allow for more precise instances with derivingVia gives...