#5770: Non-sensical 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 I compile the following code:
{{{
{-# LANGUAGE TypeFamilies,
PolyKinds,
ScopedTypeVariables
#-}
convert :: a -> b
convert = undefined
type family Foo a
type instance Foo Int = Bool
bar :: forall a b c dummya. (b -> c) -> ((Foo a) -> c)
bar f = (convert f :: (Foo a) -> c)
}}}
I get the following error message:
{{{
Sandbox.hs:13:34:
Kind mis-match
Expected kind `OpenKind', but `c' has kind `b'
In an expression type signature: (Foo a) -> c
In the expression: (convert f :: (Foo a) -> c)
In an equation for `bar': bar f = (convert f :: (Foo a) -> c)
}}}
This error message does not make sense, for 'b' isn't a kind. It is
interesting to note that removing {{{dummya}}} from the list of declared
type variables changes the error to a GHC panic.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5770>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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