[GHC] #8813: further support deriving instances Typeable1, Typeable2, etc

[GHC]

#8813: further support deriving instances Typeable1, Typeable2, etc
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        Reporter:  maeder                     |            Owner:
            Type:  task                       |           Status:  closed
        Priority:  normal                     |        Milestone:
       Component:  Compiler                   |          Version:
      Resolution:  wontfix                    |  7.8.1-rc1
Operating System:  Unknown/Multiple           |         Keywords:
 Type of failure:  GHC rejects valid program  |     Architecture:
       Test Case:                             |  Unknown/Multiple
        Blocking:                             |       Difficulty:  Unknown
                                              |       Blocked By:
                                              |  Related Tickets:
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Comment (by maeder):

 The other simple alternative is to patch the renamer and rename the class
 Data.Typeable.TypeableN to Data.Typeable.Typeable.

 This surely does not reconcile typeOF and typeRep, but hand-written
 instances have been (sort of) deprecated long before.

 I'm not familiar with the internals of Data.Typeable but the following is
 not impossible:
 {{{
  {-# Language FlexibleInstances, UndecidableInstances #-}
 class Pretty a where
   pretty :: a -> String
 instance Show a => Pretty a where
   pretty = show
 }}}

 Furthermore, Data.!OldTypeable should be removed. It's more harmful to
 provide a second incompatible Typeable class.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8813#comment:7>
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