[GHC] #11463: Template Haskell applies too many arguments to kind synonym

19 Jan 2016

      #11463: Template Haskell applies too many arguments to kind synonym
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Template       |           Version:  8.0.1-rc1
  Haskell                            |
           Keywords:  TypeInType,    |  Operating System:  Unknown/Multiple
  TypeApplications                   |
       Architecture:                 |   Type of failure:  Incorrect result
  Unknown/Multiple                   |  at runtime
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #11376
Differential Rev(s):                 |         Wiki Page:
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 Running the following code:

 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE TypeInType #-}
 module IdStarK where

 import Data.Kind
 import Language.Haskell.TH

 type Id a = a
 data Proxy (a :: Id k) = Proxy

 $(return [])

 main :: IO ()
 main = do
   putStrLn $(reify ''Proxy >>= stringE . pprint)
   putStrLn $(reify ''Proxy >>= stringE . show)
 }}}

 Gives a result I wouldn't have expected:

 {{{
 $ /opt/ghc/head/bin/runghc IdStarK.hs
 data IdStarK.Proxy (a_0 :: IdStarK.Id * k_1) = IdStarK.Proxy
 TyConI (DataD [] IdStarK.Proxy [KindedTV a_1627394516 (AppT (AppT (ConT
 IdStarK.Id) StarT) (VarT k_1627394515))] Nothing [NormalC IdStarK.Proxy
 []] [])
 }}}

 From the output, it appears that `Id` is being applied to ''two''
 arguments, both `*` and `k`! Perhaps this indirectly (or directly) a
 consequence of #11376?

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11463
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