Bugs item #1186853, was opened at 2005-04-20 18:10
Message generated for change (Comment added) made by simonpj
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Category: Compiler
Group: 6.4
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: daniel (jcpetruzza)
Assigned to: Nobody/Anonymous (nobody)
Summary: Kind error cccasionally reported
Initial Comment:
Consider an example made of the following two files:
1) TypeDefinition.hs:
module TypeDefinition (PublicType)
where
import Control.Monad.State
type PublicType a b = a String b
-- type PrivateType = PublicType StateT IO
2) Main.hs
module Main
where
import Control.Monad.State
import TypeDefinition(PublicType)
type MyType = PublicType StateT IO
main :: IO ()
main = putStrLn "Hello, world"
If I try to build Main, I get the following error:
bash-2.05b$ ghc --make Main.hs
Chasing modules from: Main.hs
Compiling TypeDefinition ( ./TypeDefinition.hs,
./TypeDefinition.o )
Compiling Main ( Main.hs, Main.o )
Main.hs:7:37:
Kind error: `StateT' is not applied to enough type
arguments
In the type synonym declaration for `MyType'
However, if one uncomments the commented line in
TypeDefinition.hs, everything builds ok (even when
PrivateType is not visible from Main)
I'm using GHC 6.4 on Mandrake 10.1
----------------------------------------------------------------------
>Comment By: Simon Peyton Jones (simonpj)
Date: 2005-04-25 08:20
Message:
Logged In: YES
user_id=50165
Simon M is exactly right. It's not a bug.
Simon PJ
----------------------------------------------------------------------
Comment By: Simon Marlow (simonmar)
Date: 2005-04-21 10:14
Message:
Logged In: YES
user_id=48280
This looks strange, but I think it's the right behaviour.
In the absence of any other information about the type
variable 'b' in your definition of PublicType, it defaults
to kind *. When you uncomment the PrivateType definition,
it is instantiated with kind (*->*), so the compiler infers
that as the kind for b.
I'll leave the bug open until Simon gets back, just in case
I'm wrong!
----------------------------------------------------------------------
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