[GHC] #10300: GHC rejects

[GHC]

#10300: GHC rejects
-------------------------------------+-------------------------------------
              Reporter:  mhwombat    |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  GHC rejects
  Unknown/Multiple                   |  valid program
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:  10020
Differential Revisions:              |
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 In GHC 7.8.4, the following code is legal:


 {{{
 {-# LANGUAGE TypeFamilies, FlexibleContexts #-}

 class FiniteGrid g where
   type Size s
   size :: g -> Size g
   maxPossibleDistance :: g -> Int

 }}}

 But with GHC 7.10.1, it no longer compiles. The error message is:


 {{{
 The associated type ‘Size’
 mentions none of the type or kind variables of the class ‘FiniteGrid g’
 In the class declaration for ‘FiniteGrid’

 }}}

 I didn't see any mention of this in the migration guide, but perhaps
 there's another pragma I need to enable. I thought this might be related
 to https://ghc.haskell.org/trac/ghc/ticket/10020, but that bug is
 apparently fixed in GHC 7.10.1.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10300>
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