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Today's Topics:
1. Trouble with liftIO in ReaderT (John Smith)
2. Re: Trouble with liftIO in ReaderT (Daniel Fischer)
3. Re: Trouble with liftIO in ReaderT (John Smith)
4. Developing dependant libraries simultaneously (John Smith)
----------------------------------------------------------------------
Message: 1
Date: Sun, 30 Jan 2011 16:16:36 +0200
From: John Smith <[email protected]>
Subject: [Haskell-beginners] Trouble with liftIO in ReaderT
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I'm trying to attach a handler to a Gtk2Hs event, and get the error:
No instance for (Control.Monad.IO.Class.MonadIO
(mtl-1.1.0.2:Control.Monad.Reader.ReaderT (GHC.Ptr.Ptr
EAny) IO))
arising from a use of `liftIO'
Possible fix:
add an instance declaration for
(Control.Monad.IO.Class.MonadIO
(mtl-1.1.0.2:Control.Monad.Reader.ReaderT (GHC.Ptr.Ptr EAny) IO))
This occurs with the sample at
http://www.haskell.org/haskellwiki/Gtk2Hs/Tutorials/Intro
import Graphics.UI.Gtk
import Control.Monad.Trans(liftIO)
main = do
initGUI
window <- windowNew
window `on` deleteEvent $ liftIO mainQuit >> return False
-- i.e., on window deleteEvent (liftIO mainQuit >> return False)
widgetShow window
mainGUI
Why can't GHC find the instance MonadIO m => MonadIO (ReaderT r m)?
------------------------------
Message: 2
Date: Sun, 30 Jan 2011 15:43:00 +0100
From: Daniel Fischer <[email protected]>
Subject: Re: [Haskell-beginners] Trouble with liftIO in ReaderT
To: [email protected]
Cc: John Smith <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
On Sunday 30 January 2011 15:16:36, John Smith wrote:
> I'm trying to attach a handler to a Gtk2Hs event, and get the error:
>
> No instance for (Control.Monad.IO.Class.MonadIO
> (mtl-1.1.0.2:Control.Monad.Reader.ReaderT
> (GHC.Ptr.Ptr EAny) IO)) arising from a use of `liftIO'
> Possible fix:
> add an instance declaration for
> (Control.Monad.IO.Class.MonadIO
> (mtl-1.1.0.2:Control.Monad.Reader.ReaderT (GHC.Ptr.Ptr EAny) IO))
>
> This occurs with the sample at
> http://www.haskell.org/haskellwiki/Gtk2Hs/Tutorials/Intro
>
> import Graphics.UI.Gtk
> import Control.Monad.Trans(liftIO)
>
> main = do
> initGUI
> window <- windowNew
> window `on` deleteEvent $ liftIO mainQuit >> return False
> -- i.e., on window deleteEvent (liftIO mainQuit >> return False)
> widgetShow window
> mainGUI
>
> Why can't GHC find the instance MonadIO m => MonadIO (ReaderT r m)?
>
GHC specifies the package the offending ReaderT comes from, mtl-1.1.0.2.
mtl-1.1.0.2's ReaderT is an instance of mtl-1.1.0.2's MonadIO class. That
class was defined in Control.Monad.Trans.
Note that
a) the package from which the MonadIO class in the error message comes is
not specified,
b) it is qualified as Control.Monad.IO.Class.MonadIO, it comes from a
module of the transformers package.
I suspect that your programme uses inconsistent dependencies, some part of
it was built against mtl-1.1.0.2, some other part uses mtl-2.* (which is a
wrapper around transformers, exporting mtl's old API [with a few
differences]) or transformers directly.
Check which mtl-version gtk2hs was built against (
$ ghc-pkg describe gtk
, look at the depends field fairly low down), probably that was built
against mtl-1.1.0.2.
To fix it you can
- maybe rebuild gtk2hs (gtk, glade, pango, ...) against mtl-2 [much
compiling, may not work, but would save some headaches later if it does]
- build your programme against mtl-1.1.0.2 (either by writing a .cabal file
specifying mtl-1 or by passing -package mtl-1.1.0.2 on the command line).
HTH,
Daniel
------------------------------
Message: 3
Date: Sun, 30 Jan 2011 21:16:43 +0200
From: John Smith <[email protected]>
Subject: Re: [Haskell-beginners] Trouble with liftIO in ReaderT
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 30/01/2011 16:43, Daniel Fischer wrote:
> On Sunday 30 January 2011 15:16:36, John Smith wrote:
>> I'm trying to attach a handler to a Gtk2Hs event, and get the error:
>>
>> No instance for (Control.Monad.IO.Class.MonadIO
>> (mtl-1.1.0.2:Control.Monad.Reader.ReaderT
>> (GHC.Ptr.Ptr EAny) IO)) arising from a use of `liftIO'
>> Possible fix:
>> add an instance declaration for
>> (Control.Monad.IO.Class.MonadIO
>> (mtl-1.1.0.2:Control.Monad.Reader.ReaderT (GHC.Ptr.Ptr EAny) IO))
>>
>> This occurs with the sample at
>> http://www.haskell.org/haskellwiki/Gtk2Hs/Tutorials/Intro
>>
>> import Graphics.UI.Gtk
>> import Control.Monad.Trans(liftIO)
>>
>> main = do
>> initGUI
>> window<- windowNew
>> window `on` deleteEvent $ liftIO mainQuit>> return False
>> -- i.e., on window deleteEvent (liftIO mainQuit>> return False)
>> widgetShow window
>> mainGUI
>>
>> Why can't GHC find the instance MonadIO m => MonadIO (ReaderT r m)?
>>
>
> GHC specifies the package the offending ReaderT comes from, mtl-1.1.0.2.
> mtl-1.1.0.2's ReaderT is an instance of mtl-1.1.0.2's MonadIO class. That
> class was defined in Control.Monad.Trans.
>
> Note that
> a) the package from which the MonadIO class in the error message comes is
> not specified,
> b) it is qualified as Control.Monad.IO.Class.MonadIO, it comes from a
> module of the transformers package.
>
> I suspect that your programme uses inconsistent dependencies, some part of
> it was built against mtl-1.1.0.2, some other part uses mtl-2.* (which is a
> wrapper around transformers, exporting mtl's old API [with a few
> differences]) or transformers directly.
>
> Check which mtl-version gtk2hs was built against (
> $ ghc-pkg describe gtk
> , look at the depends field fairly low down), probably that was built
> against mtl-1.1.0.2.
>
> To fix it you can
> - maybe rebuild gtk2hs (gtk, glade, pango, ...) against mtl-2 [much
> compiling, may not work, but would save some headaches later if it does]
> - build your programme against mtl-1.1.0.2 (either by writing a .cabal file
> specifying mtl-1 or by passing -package mtl-1.1.0.2 on the command line).
>
> HTH,
> Daniel
I had mtl-1 as a system package, and mtl-2 as a user package. I forced the
removal of mtl-1, reinstalled gtk (and a few
other things), and it's working now.
Thank you.
------------------------------
Message: 4
Date: Sun, 30 Jan 2011 22:42:58 +0200
From: John Smith <[email protected]>
Subject: [Haskell-beginners] Developing dependant libraries
simultaneously
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I am working on libraries A, B, and C simultaneously. B and C both depend on A.
Whenever A changes, I have to rebuild an
reinstall it for the changes to be picked up by B and C.
Is there any way to tell cabal or GHC that B and C should import A, and check
for changes when building? I'm using
EclipseFP, but adding a project-reference does not appear to have any effect.
------------------------------
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