Re: [Haskell-cafe] Incompatibility of different (monad transformer) libraries
On Sat, 14 Mar 2009 02:14:53 +0100 (CET), Henning Thielemann lemm...@henning-thielemann.de wrote: I think 'transformers' exports Control.Monad.Trans.State. This should not conflict with MTL. However, MTL's State type is different from transformer's one. Is that your problem? No. The immediate problem is, that a module named Control.Monad.State is exported by both mtl and monads-tf (and my code needs both packages). It is indeed unfortunate that mtl:State is a different type from transformers:State, but that is not biting me right now. Since the 'cabal' tool became better and better, today I use a cabal file even for small programs. Cabal automatically calls GHC with the right package exposing and hiding options. I already use cabal; my own package has mtl, transformers and monads-tf among its dependencies. Regards, Arie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Incompatibility of different (monad transformer) libraries
On Mon, Mar 16, 2009 at 9:26 AM, Arie Peterson ar...@xs4all.nl wrote: It is indeed unfortunate that mtl:State is a different type from transformers:State, but that is not biting me right now. If the type problem does ever become an issue, could the MTL use the types from the transformers package? Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Incompatibility of different (monad transformer) libraries
On Tue, 10 Mar 2009, ariep wrote:
Problem instance
In my code, I use some monad transformers. I used to use the mtl package,
but I recently switched to the combination transformers/monads-tf
(mainly for the Applicative instances).
The same code also uses the haskeline library, for line reading.
Haskeline allows to edit the user's history (previously entered lines), but
only through a Control.Monad.State interface, and that happens to be the
Control.Monad.State from mtl. So now, my package also needs to import
mtl.
This combination of package dependencies gives import conflicts: whenever I
import some Control.Monad.{State,Error,Cont,...} module, there is more than
one package providing such a module.
I think 'transformers' exports Control.Monad.Trans.State. This should not
conflict with MTL. However, MTL's State type is different from
transformer's one. Is that your problem?
Solution?
For now, I resolve the ambiguity by using Package imports, i.e. annotate
the ambiguous imports by the right package name.
Is this the best solution? The ghc manual states, that the package import
extension should not be necessary. I can think of another solution, by
creating a dedicated package, which imports mtl:Control.Monad.* and
re-exports them under another name, but that's even less elegant than
package imports.
Since the 'cabal' tool became better and better, today I use a cabal file
even for small programs. Cabal automatically calls GHC with the right
package exposing and hiding options.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Incompatibility of different (monad transformer) libraries
Hi,
Problem instance
In my code, I use some monad transformers. I used to use the mtl package,
but I recently switched to the combination transformers/monads-tf
(mainly for the Applicative instances).
The same code also uses the haskeline library, for line reading.
Haskeline allows to edit the user's history (previously entered lines), but
only through a Control.Monad.State interface, and that happens to be the
Control.Monad.State from mtl. So now, my package also needs to import
mtl.
This combination of package dependencies gives import conflicts: whenever I
import some Control.Monad.{State,Error,Cont,...} module, there is more than
one package providing such a module.
Solution?
For now, I resolve the ambiguity by using Package imports, i.e. annotate
the ambiguous imports by the right package name.
Is this the best solution? The ghc manual states, that the package import
extension should not be necessary. I can think of another solution, by
creating a dedicated package, which imports mtl:Control.Monad.* and
re-exports them under another name, but that's even less elegant than
package imports.
What is the recommended way to deal with module name conflicts, such as
this one?
Regards,
Arie
BTW: how can I let the user edit a line of text, from a non-empty starting
value for the text? (In other words, actually *edit* a line, not enter a
new one.) I currently do this by adding the starting value to the user's
history, so he/she can get it by pressing the up arrow key. This is clearly
not optimal.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
