[GHC] #8953: Reifying poly-kinded type families misses kind annotations

3 Apr 2014

      #8953: Reifying poly-kinded type families misses kind annotations
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       Reporter:  goldfire          |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Template Haskell  |           Version:  7.9
       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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 Consider the following two modules:

 {{{
 {-# LANGUAGE DataKinds, PolyKinds, TypeFamilies #-}

 module A where

 type family Poly (a :: k) :: *
 type instance Poly (x :: Bool) = Int
 type instance Poly (x :: Maybe k) = Double
 }}}

 {{{
 {-# LANGUAGE TemplateHaskell #-}

 module B where

 import Language.Haskell.TH
 import A

 $( do info <- reify ''Poly
       runIO $ putStrLn $ pprint info
       return [] )
 }}}

 Compiling with HEAD yields this output:

 {{{
 type family A.Poly (a_0 :: k_1) :: *
 type instance A.Poly x_2 = GHC.Types.Double
 type instance A.Poly x_3 = GHC.Types.Int
 }}}

 The problem is that the type patterns in the reified instances are just
 plain variables, without their kind annotations. This omission makes the
 instance declarations unfaithful to the original meaning.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8953
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