Re: [GHC] #10403: GHC crashes on a partial type signature

11 May 2015


      #10403: GHC crashes on a partial type signature
-------------------------------------+-------------------------------------
        Reporter:  Artyom.Kazak      |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Linux             |            Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash                              |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------
Description changed by Artyom.Kazak:

Old description:
...
The following code crashes GHC 7.10.1 as is, but doesn't result in a
crash if the signature is specified completely or isn't specified at all
(inferred):
{{{#!hs
{-# LANGUAGE PartialTypeSignatures #-}
module Main where
data I a = I a
instance Functor I where
    fmap f (I a) = I (f a)
newtype B t a = B a
instance Functor (B t) where
    fmap f (B a) = B (f a)
newtype H f = H (f ())
app :: H (B t)
app = h (H . I) (B ())
h :: _
--h :: Functor m => (a -> b) -> m a -> H m
h f b = (H . fmap (const ())) (fmap f b)
}}}
New description:

 The following code crashes GHC 7.10.1 as is, but doesn't result in a crash
 if the signature is specified completely or isn't specified at all
 (inferred):

 {{{#!hs
 {-# LANGUAGE PartialTypeSignatures #-}
 module Main where

 main :: IO ()
 main = return ()

 data I a = I a
 instance Functor I where
     fmap f (I a) = I (f a)

 newtype B t a = B a
 instance Functor (B t) where
     fmap f (B a) = B (f a)

 newtype H f = H (f ())

 app :: H (B t)
 app = h (H . I) (B ())

 h :: _
 --h :: Functor m => (a -> b) -> m a -> H m
 h f b = (H . fmap (const ())) (fmap f b)
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10403#comment:2
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