[GHC] #13368: Derive superclasses automatically if possible

[GHC]

#13368: Derive superclasses automatically if possible
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #10607
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 So I don't forget, this is like #10607 along another axis.

 Instead of writing

 {{{#!hs
 newtype IO_ a = IO_ (IO a)
   deriving newtype (Functor, Applicative, Monad, MonadIO)
 }}}

 allow writing

 {{{#!hs
 newtype IO_ a = IO_ (IO a)
   deriving newtype MonadIO
 }}}

 with the same meaning, are there any technical restrictions to this? This
 gets annoying in large hierarchies where you need `Eq`, `Ord`, `Num`,
 `Fractional`, `Floating`, `Real` and `RealFrac` just to derive

 {{{#!hs
 newtype F32 = F32 Float
   deriving newtype RealFloat
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13368>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler