Documentation of CoAxiom: saturation and roles
The documentation around CoAxiom has a couple of problems: It is inconsistently claimed that
- CoAxioms are applied to Nominal coercions only (https://gitlab.haskell.org/ghc/ghc/blob/master/compiler/types/TyCoRep.hs#L1196),
- and also that they have role annotations similar to TyCons (https://gitlab.haskell.org/ghc/ghc/blob/master/compiler/types/CoAxiom.hs#L333).
I think the second of these is the correct one.
Secondly, the note [CoAxiom saturation] (https://gitlab.haskell.org/ghc/ghc/blob/master/compiler/types/CoAxiom.hs#L313) is rather truncated, and I couldn't see anything in the git history that should have gone there
Environment
- GHC version used: 8.6.5, master