On Tue, 2008-04-29 at 17:59 -0400, Yaakov Nemoy wrote:
Hi List,
First off, I want to say hi, as this is my first post. I'm trying to get some badly needed updates to cabal-rpm, so we can get more Haskell packages into Fedora.
Great! :-)
All of the following is with Cabal 1.2.3.0 and GHC 6.8.2 as packaged in Fedora 8.
In the module Distribution.PackageDescription, there are four functions, hasExes, and hasLibs, as well as libModules and exeModules. These functions claim to do the obvious for a PackageDescription. The only problem I'm having is with packages like xmonad, which have both Executables and Libraries.
In the case of xmobar, hasLibs returns False, and an empty list for libModules, but True and a list for hasExes and exeModules respectively.
This is as you expect right? The xmobar package contains one exe.
In the case of xmonad-contrib, the opposite is true, that is there are no Executables at all, but a bucket load of Libraries.
Yes.
In the case of xmonad, hasLibs returns True. but returns a nonempty list. hasExes returns True, and with the same nonempty list. I would expect the lists to be the same, as all the Modules listed therein are needed to compile the executable, and also to be linked with the user supplied config file. The only problem I see is with hasLibs itself.
http://hackage.haskell.org/packages/archive/xmonad/0.7/xmonad.cabal Looking at the xmonad.cabal file we see that xmonad does contain both a library and an executable, so we would expect hasLibs and hasExes to return True. The reason the modules returned for both are the same is because the list of exposed-modules and other-modules in the xmonad.cabal are exactly the same for the lib and for the exe.
I heard something a while back that xmonad needs to be compiled twice, because this setup is considered an edge case in Cabal. Because xmonad is the reason why I'm working on getting Haskell packages into Fedora, I'm not sure I want to think of it that way. Is this a bug, or just a 'feature' I need to watch out for?
What they meant is that it is not currently possible to make a package with a library and an executable where the executable links against the library, instead it must compile the same modules that are in the library itself. So that's what people mean by having to compile things twice. If/when it becomes possible we'd write something like: library exposed-modules: XMonad XMonad.Main [...etc...] executable xmonad main-is: Main.hs build-depends: xmonad [...etc...] That is, we'd specify that the xmonad depends on the xmonad library. Then it would not be necessary to list all the modules twice and have them compiled twice. So in summary: there is no bug. xmonad really does contain a library and an executable. The only limitation is that a few modules get compiled twice rather than once. Duncan