[GHC] #15310: Derive Generic1 instances for types of kind (k -> *) -> * that include applications of the parameter

[GHC]

#15310: Derive Generic1 instances for types of kind (k -> *) -> * that include
applications of the parameter
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        Reporter:  cedricshock       |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler (Type    |              Version:
  checker)                           |             Keywords:  DeriveGeneric
      Resolution:                    |  Generic1
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by cedricshock):

 I wrote an implementation of `Generic1` deriving using `ParAp0` and
 `ParAp1`. You can preview it in this PR:
 https://github.com/Cedev/ghc/pull/1

 I could use some practical advice and help on what to do next

   1. I don't have a test case for a kind `(k -> *) -> *` where `k` isn't
 `*`. If you have any ideas, especially for a test case where `k ~
 Constraint`, I'd appreciate them.

   2. There are types in `base` that can now have `Generic1` instances
 derived for them, starting with `ParAp0` and `ParAp1` themselves. How do I
 add `Generic1` instances to base without breaking the compiler building,
 since an old compiler won't be able to derive those `Generic1` instances?

   3. What other typeclasses should `ParAp0` and `ParAp1` have instances
 for?

   4. What do I do next? Get feedback from both `ghc-devs` and `glasgow-
 haskell-users`?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15310#comment:2>
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