[GHC] #7536: Panic with TypeFamilies with type synonym instances

[GHC]

#7536: Panic with TypeFamilies with type synonym instances
-------------------------------+--------------------------------------------
Reporter:  snowleopard         |          Owner:                  
    Type:  bug                 |         Status:  new             
Priority:  normal              |      Component:  Compiler        
 Version:  7.6.1               |       Keywords:                  
      Os:  Unknown/Multiple    |   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |      Blockedby:                  
Blocking:                      |        Related:                  
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Comment(by simonpj@…):

 commit e89f3bac94f513841f46346528183920783ce1f9
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Wed Jan 2 08:26:28 2013 +0000

     In type or data instances, check that all variables are bound

     Trac #7536 points out that it's possible for the LHS to *look*
     as if it binds variables, but does not acutally do so

              type T a = Int
              type instance F (T a) = a

     This patch makes it an error.

  compiler/typecheck/TcInstDcls.lhs   |   43
 ++++++++++++++++++-----------------
  compiler/typecheck/TcMType.lhs      |   36 ++++++++++++++++++++++-------
  compiler/typecheck/TcTyClsDecls.lhs |   23 ++++++------------
  3 files changed, 57 insertions(+), 45 deletions(-)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7536#comment:2>
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