[GHC] #13092: family instance consistency checks are too pessimistic

[GHC]

#13092: family instance consistency checks are too pessimistic
-------------------------------------+-------------------------------------
        Reporter:  rwbarton          |                Owner:  rwbarton
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by goldfire):

 Replying to [comment:5 simonpj]:
 > Actually there is ''some'' justification for the status quo.

 ... except that, regardless of Reid's excellent example in comment:6,
 having `F Int = Bool` and `F Int = Char` in scope means that we can write
 a proof of `Bool ~ Char` in Core. Continuing the status quo means that
 Core Lint is much less useful.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13092#comment:10>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler