#5769: Incorrect error message when compiling with PolyKinds and a type family
------------------------------+---------------------------------------------
Reporter: goldfire | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 7.4.1-rc1 | Keywords: PolyKinds
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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When trying to compile
{{{
{-# LANGUAGE TypeFamilies,
PolyKinds,
ScopedTypeVariables
#-}
convert :: a -> b
convert = undefined
type family Foo a
bar :: forall b a. b -> (Foo a)
bar f = (convert f :: (Foo a))
}}}
I get the following error message:
{{{
Sandbox.hs:12:10:
Couldn't match type `Foo k a' with `Foo * b'
NB: `Foo' is a type function, and may not be injective
In the expression: (convert f :: Foo a)
In an equation for `bar': bar f = (convert f :: Foo a)
}}}
However, this compiles just fine without {{{PolyKinds}}}.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5769>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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