#4008: type error trying to specialize polymorphic function
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Reporter: nr | Owner: simonpj
Type: bug | Status: new
Priority: normal | Milestone: 6.14.1
Component: Compiler (Type checker) | Version: 6.12.1
Keywords: | Difficulty:
Os: Linux | Testcase:
Architecture: x86 | Failure: GHC rejects valid
program
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Changes (by igloo):
* owner: => simonpj
* milestone: => 6.14.1
Comment:
Slightly simplified:
{{{
{-# LANGUAGE RankNTypes, EmptyDataDecls, LiberalTypeSynonyms #-}
module Pain
where
data O
data C
type Counter n e x = n e x -> Int
scalar :: (forall e x . a e x)
-> (a C O, a O O, a O C)
scalar z = (z, z, z)
wrap :: (forall e x . Counter n e x)
-> (Counter n C O, Counter n O O, Counter n O C)
wrap = scalar
}}}
with HEAD:
{{{
Pain.hs:17:8:
Couldn't match expected type `n C O' against inferred type `C'
Expected type: (Counter n C O, Counter n O O, Counter n O C)
Inferred type: (C -> O, O -> O, O -> C)
In the expression: scalar
In the definition of `wrap': wrap = scalar
}}}
(`LiberalTypeSynonyms` is actually no longer needed).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4008#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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