[GHC] #8950: Typeable instances for promoted lists and tuples

[GHC]

#8950: Typeable instances for promoted lists and tuples
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        Reporter:  kosmikus          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  libraries/base    |          Version:  7.8.1-rc2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by kosmikus):

 Just to clarify: `Typeable` works fine if I promote my own datatypes. It
 just doesn't work for the built-in lists and tuples. For example, this
 variant of my program above compiles fine:
 {{{
 {-# LANGUAGE DataKinds, KindSignatures, PolyKinds, AutoDeriveTypeable,
 TypeOperators #-}

 import Data.Proxy
 import Data.Typeable

 data Foo (xs :: MyList *) (p :: MyPair * *)

 data MyList a = Cons a (MyList a) | Nil
 data MyPair a b = MyPair a b

 main :: IO ()
 main = print (typeRep (Proxy :: Proxy (Foo (Int `Cons` Nil) ('MyPair Bool
 Char))))
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8950#comment:2>
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