[GHC] #8142: Panic on TypeFamilies compile

[GHC]

#8142: Panic on TypeFamilies compile
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       Reporter:  zenzike          |             Owner:
           Type:  bug              |            Status:  new
       Priority:  normal           |         Milestone:
      Component:  Compiler         |           Version:  7.6.3
       Keywords:                   |  Operating System:  MacOS X
   Architecture:                   |   Type of failure:  Compile-time crash
  Unknown/Multiple                 |         Test Case:
     Difficulty:  Unknown          |          Blocking:
     Blocked By:                   |
Related Tickets:                   |
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 The following code produces a panic:
 {{{
 > {-# LANGUAGE TypeFamilies #-}

 > module Bug where

 > tracer :: (Functor f, Coinductive f) => (c -> f c) -> (c -> f c)
 > tracer = h where h = (\(_, b) -> ((outI . fmap h) b)) . out

 > class Functor g => Coinductive g where
 >   type Nu g :: *
 >   out     :: Nu g -> g (Nu g)
 >   outI    :: g (Nu g) -> Nu g
 }}}
 Compiling with ghc-7.6.3 gives:
 {{{
 $ ghc Bug.lhs
 [1 of 1] Compiling Bug              ( Bug.lhs, Bug.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.6.3 for x86_64-apple-darwin):
         cgLookupPanic (probably invalid Core; try -dcore-lint)
     h{v aeN} [lid]
     static binds for:
     local binds for:
     main:Bug.outI{v r0} [gid[ClassOp]]
     main:Bug.out{v r1} [gid[ClassOp]]
     main:Bug.$p1Coinductive{v reT} [gid[ClassOp]]

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8142>
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