[GHC] #8135: Panic when printing out kind incompatibility error

[GHC]

#8135: Panic when printing out kind incompatibility error
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       Reporter:  Saulzar           |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.6.2
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I wrote a little utility function against the new pipes 4.0 repository but
 neglected to put the brackets around lift (f x)  like so:

 mapM :: (Monad m) => (a -> m b) -> Pipe a b m r
 mapM f =  for cat $ \x -> do
   r <- lift f x
   yield r

 Which resulted in this error/panic.

 src/Utils/Pipes.hs:13:8:
     Couldn't match kind `* -> *' with `*'
     Expected type: a -> Proxy () a () b m b
       Actual type: a -> Proxy () a () b m b
     Kind incompatibility when matching types:
       a :: * -> *
       a :: *
     The function `lift'ghc: panic! (the 'impossible' happened)
   (GHC version 7.6.2 for x86_64-unknown-linux):
         kindFunResult ghc-prim:GHC.Prim.*{(w) tc 34d}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8135>
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