#11135: Migrate more of Data.Functor.* from transformers to base. -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: task | Status: upstream Priority: highest | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1543 Wiki Page: | Phab:D1544 Phab:D1630 -------------------------------------+------------------------------------- Comment (by duairc): While I can see how the `Eq1`, `Ord1`, `Read1` and `Show1` classes could be useful in their own right, is it set in stone that the `Eq`, `Ord`, `Read` and `Show` instances of the various functors must use them? Why can't the `Eq` instance for `Compose` just be `Eq (f (g a)) => Eq (Compose f g a)`? Do we care about Haskell98 compatibility in `base`? I don't have a strong opinion either way for `Eq`, `Ord`, `Read` and `Show`, but I would slightly prefer instances of the form I have above. What I'm really interested in is the other type classes for which the functors could have instances. Do we need to make a `Semigroup1`, a `Monoid1` if we want to make `Compose` an instance of `Semigroup` and `Monoid`? What about a `Storable1`? Or can we just make an instance `Storable (f (g a)) => Eq (Compose f g a)`? I would basically like to make as many of these instances as possible, because I'm working on something at the moment that uses a lot of functors and potentially compositions of functors, but I want to "keep" as many of the instances of my base types as possible. I'd be happy to do up a patch that made as many of these instances as possible, but I'm wondering would I be expected to make all those extra classes, or could I just make the non-Haskell98 instances? And if so, is there any good reason not to just do the same for `Eq`, `Ord`, `Read` and `Show`? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11135#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler