Re: [GHC] #14164: GHC hangs on type family dependency

2 Jun 2018

      #14164: GHC hangs on type family dependency
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
                                     |  InjectiveFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Here's a somewhat smaller example that also loops at compile-time:

 {{{#!hs
 {-# LANGUAGE TypeFamilyDependencies #-}
 {-# LANGUAGE TypeInType #-}
 {-# LANGUAGE TypeOperators #-}
 module Bug where

 data G (x :: a) = GNil | GCons (G x)

 type family F (xs :: [a]) (g :: G (z :: a)) = (res :: [a]) | res -> a
 where
   F (x:xs) GNil         = x:xs
   F (x:xs) (GCons rest) = x:F xs rest
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14164#comment:4
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