[GHC] #12522: GHC 8.0.1 hangs, looping forever in type-checker

[GHC]

#12522: GHC 8.0.1 hangs, looping forever in type-checker
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        Reporter:  clinton           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by andreash):

 I think I may just have hit the same bug.

 I've extracted a small example:


 {{{#!hs
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE TypeFamilyDependencies #-}
 {-# LANGUAGE TypeOperators #-}

 newtype I a = I a

 type family Curry (as :: [*]) b = f | f -> as b where
     Curry '[] b = I b
     Curry (a:as) b = a -> Curry as b

 data Uncurried (as :: [*]) b

 def :: Curry as b -> Uncurried as b
 def = undefined

 test :: Uncurried [Int, String] String
 test = def $ \n s -> I $ show n ++ s

 test2 :: Uncurried [Bool, Bool] Bool
 test2 = def $ \a b -> I $ a && b
 }}}

 Removing the type signatures from either `test`, or `test2` will hang ghc.
 If the type family is not defined as injective, then ghc doesn't hang, but
 instead gives an error message about ambiguous type variables.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12522#comment:15>
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