Hi all, I've just received the following error message: headers.hs:6:7: Could not find module `Control.Monad.Identity': it was found in multiple packages: transformers-0.1.4.0 mtl-1.1.0.2 I'm trying to use the Iteratee module which depends on Transformers but I use MTL in other stuff. Whats the preferred solution here? Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/
ghc-pkg hide transformers On Oct 12, 2009, at 5:46 PM, Erik de Castro Lopo wrote:
Hi all,
I've just received the following error message:
headers.hs:6:7: Could not find module `Control.Monad.Identity': it was found in multiple packages: transformers-0.1.4.0 mtl-1.1.0.2
I'm trying to use the Iteratee module which depends on Transformers but I use MTL in other stuff.
Whats the preferred solution here?
Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Gregory Crosswhite wrote:
ghc-pkg hide transformers
Here's an example. CGI uses MTL, Iteratee uses Transformers. So, how do you use CGI and Iteratee in the same program? Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/
Erik de Castro Lopo wrote:
Gregory Crosswhite wrote:
ghc-pkg hide transformers
Here's an example. CGI uses MTL, Iteratee uses Transformers.
So, how do you use CGI and Iteratee in the same program?
CGI is just one of many examples. Text.Regex, Network.HTTP, Database.HDBS.Sqlite, Tagsoup are others. Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/
Ugh, I'm not as sure about that... it took me long enough just to figure out "ghc-pkg hide transformers"! :-) Are running into problems because you need to refer to both packages (e.g., mtl and transformers) within your code, or because you are using packages that refer to each? Because as long as you only need to refer to one of them in your own code, GHC should be able to handle the dependencies for the other packages correctly. (Hiding the package only removes it from being automatically imported by your own code, it doesn't prevent it from being used by other packages that link to it.) Cheers, Greg On Oct 12, 2009, at 6:08 PM, Erik de Castro Lopo wrote:
Gregory Crosswhite wrote:
ghc-pkg hide transformers
Here's an example. CGI uses MTL, Iteratee uses Transformers.
So, how do you use CGI and Iteratee in the same program?
Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Gregory Crosswhite wrote:
Are running into problems because you need to refer to both packages (e.g., mtl and transformers) within your code, or because you are using packages that refer to each?
The later. Iteratee uses Transformers and just about everything else I want to use uses MTL.
Because as long as you only need to refer to one of them in your own code, GHC should be able to handle the dependencies for the other packages correctly. (Hiding the package only removes it from being automatically imported by your own code, it doesn't prevent it from being used by other packages that link to it.)
That all seems a little hackish. However after reading the hackage descriptions of both Transformers and MTL, it seems that they share a very similar heritage. I therefore hacked the iteratee.cabal file and replaced the build-depends on transformers with one on mtl and the package built quite happily. I'll play with it a bit to see if its working correctly. Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/
Erik de Castro Lopo wrote:
However after reading the hackage descriptions of both Transformers and MTL, it seems that they share a very similar heritage. I therefore hacked the iteratee.cabal file and replaced the build-depends on transformers with one on mtl and the package built quite happily. I'll play with it a bit to see if its working correctly.
I think the standard solutions are * use Cabal for your project and/or * use the PackageImports extension. HTH, Martijn.
Erik de Castro Lopo wrote:
However after reading the hackage descriptions of both Transformers and MTL, it seems that they share a very similar heritage. I therefore hacked the iteratee.cabal file and replaced the build-depends on transformers with one on mtl and the package built quite happily. I'll play with it a bit to see if its working correctly.
Well Iteratee built with MTL passes all the tests that shipped with it so I suppose it must be correct. Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/
On Tue, Oct 13, 2009 at 12:08:21PM +1100, Erik de Castro Lopo wrote:
Here's an example. CGI uses MTL, Iteratee uses Transformers.
So, how do you use CGI and Iteratee in the same program?
There should be no problem with that, as long as you build your program using cabal. Cabal will build each package exposing only the packages it directly depends on.
On Tue, Oct 13, 2009 at 08:43:12AM +0100, Ross Paterson wrote:
On Tue, Oct 13, 2009 at 12:08:21PM +1100, Erik de Castro Lopo wrote:
Here's an example. CGI uses MTL, Iteratee uses Transformers.
So, how do you use CGI and Iteratee in the same program?
There should be no problem with that, as long as you build your program using cabal. Cabal will build each package exposing only the packages it directly depends on.
Ah, I see: both packages have MonadIO and MonadTrans in their interface. That will be a problem, which will only be fixed by the proposed transition Ganesh mentioned.
On Tuesday 13 October 2009 02:46:29 Erik de Castro Lopo wrote:
Hi all,
I've just received the following error message:
headers.hs:6:7: Could not find module `Control.Monad.Identity': it was found in multiple packages: transformers-0.1.4.0 mtl-1.1.0.2
I'm trying to use the Iteratee module which depends on Transformers but I use MTL in other stuff.
Whats the preferred solution here?
Erik
Hi, alternative to ghc-pkg: {-# LANGUAGE -XPackageImports #-} module Blub where import "mtl" Control.Monad.State -- Daniel
participants (5)
-
Daniel Schüssler -
Erik de Castro Lopo -
Gregory Crosswhite -
Martijn van Steenbergen -
Ross Paterson