#7420: mis-attributed kind in the explict type/kind signature
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.4.2 | Keywords:
Os: FreeBSD | Architecture: x86_64 (amd64)
Failure: GHC rejects valid program | Blockedby:
Blocking: | Related:
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The following simple code
{-# LANGUAGE DataKinds #-}[[BR]]
{-# LANGUAGE KindSignatures #-}[[BR]]
{-# LANGUAGE PolyKinds #-}[[BR]]
{-# LANGUAGE ScopedTypeVariables #-}[[BR]]
data Proxy tp
hUpdateAtLabel :: forall l (n::Bool) v. v -> () -> ()
hUpdateAtLabel _ () = undefined (undefined::Proxy (n::Bool))
fails to type-check. The error message betrays a deep confusion in the
kind checker:
/tmp/s3.hs:9:52:
Kind mis-match
An enclosing kind signature specified kind `Bool',
but `n' has kind `l'
In an expression type signature: Proxy (n :: Bool)
In the first argument of `undefined', namely
`(undefined :: Proxy (n :: Bool))'
In the expression: undefined (undefined :: Proxy (n :: Bool))
If I write
hUpdateAtLabel :: forall (l :: *) (n::Bool) v. v -> () -> ()
hUpdateAtLabel _ () = undefined (undefined::Proxy (n::Bool))
the code type-checks. However,
hUpdateAtLabel :: forall l1 (l :: *) (n::Bool) v. v -> () -> ()
hUpdateAtLabel _ () = undefined (undefined::Proxy (n::Bool))
reports an error
Kind mis-match
An enclosing kind signature specified kind `Bool',
but `n' has kind `*'
It looks like an off-by-one error, at least in the error message.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7420>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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