[GHC] #9582: Associated Type Synonyms do not unfold in InstanceSigs

12 Sep 2014


      #9582: Associated Type Synonyms do not unfold in InstanceSigs
-------------------------------------+-------------------------------------
       Reporter:  andreas.abel       |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler (Type     |                 Version:  7.8.3
  checker)                           |        Operating System:
       Keywords:  InstanceSigs       |  Unknown/Multiple
  TypeFamilies                       |         Type of failure:
   Architecture:  Unknown/Multiple   |  None/Unknown
     Difficulty:  Unknown            |               Test Case:
     Blocked By:                     |                Blocking:
Related Tickets:                     |  Differential Revisions:
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 {{{#!hs
 {-# LANGUAGE InstanceSigs, TypeFamilies #-}

 class C a where
   type T a
   m :: T a

 instance C Int where
   type T Int = String
   m :: String
   m = "bla"

 -- Method signature does not match class; it should be m :: T Int
 --    In the instance declaration for ‘C Int’
 }}}

 As {{{T Int}}} is a synonym of {{{String}}}, {{{m :: String}}} should be a
 valid type signature alternative to {{{m :: T Int}}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9582
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