[GHC] #13537: Adding underscore (m :: _) to pattern variable makes it fail
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Thu Apr 6 07:06:00 UTC 2017
#13537: Adding underscore (m :: _) to pattern variable makes it fail
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Reporter: Iceland_jack | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type | Version: 8.0.1
checker) |
Resolution: | Keywords:
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 Iceland_jack):
And giving `\c -> m (c . d)` a name (without a type signature, I'm don't
have enough bravery to attempt that so early in the morning) doesn't work,
I don't know if intended behaviour or not
{{{#!hs
fmap' :: (f ~> f') -> (CodTy f -> CodTy f')
fmap' f (CodTy m) = CodTy a where
a c = m (c . f)
fmap' f (CodTy m) = let
a c = m (f . g)
in CodTy a
fmap' f (CodTy m) = do
let a c = m (f . g)
CodTy a
}}}
Okay never mind I worked it out, this works
{{{#!hs
fmap' :: forall f f'. (f ~> f') -> (CodTy f -> CodTy f')
fmap' f (CodTy (m :: forall r'. (f ty -> r') -> r')) = CodTy a where
a :: forall r. (f' ty -> r) -> r
a c = m (c . f)
}}}
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13537#comment:1>
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