[GHC] #11548: Absolutely misleading error message on kind error

6 Feb 2016


      #11548: Absolutely misleading error message on kind error
-------------------------------------+-------------------------------------
           Reporter:  mniip          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect
  Unknown/Multiple                   |  warning at compile-time
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{#!hs
 module Bug where

 import Data.Proxy

 fun :: Proxy a -> ()
 fun Proxy = ()

 bug :: ()
 bug = fun (Proxy :: Proxy Maybe)
 }}}

 {{{#!hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

 Bug.hs:9:12: error:
     • Expected kind ‘Proxy Maybe’,
         but ‘Data.Proxy.Proxy :: Proxy Maybe’ has kind ‘Proxy Maybe’
     • In the first argument of ‘fun’, namely ‘(Proxy :: Proxy Maybe)’
       In the expression: fun (Proxy :: Proxy Maybe)
       In an equation for ‘bug’: bug = fun (Proxy :: Proxy Maybe)
 }}}

 7.10 gives the appropriate `Couldn't match kind ‘* -> *’ with ‘*’`
 message.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11548
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