Upgrading Haskell Platform on openSUSE

New version of Haskell Platform has been released just a few days ago. It ships with the latest stable version of GHC (7.4.1). Here you can find release notes describing changes made to the compiler. The list is long and I haven’t read all of it but among the most important changes are:

• the possibility of entering any top-level declarations in GHCi;
• Num type class no longer has Eq and Show as its superclass;
• Data Parallel Haskell has been improved

Three months ago I wrote about installing Haskell Platform on openSUSE. I recommended that GHC be installed from precompiled binaries and the platform be installed from sources, instead of using packages from repository. Now that the new version is out this post needs an addendum about updating the platform. If the Platform was installed from the repo using a package manager everything would be simple¹. An update of packages would be enough, providing that they were updated by the maintainers of the repository (at the moment packages for openSUSE still contain older version of the platform). With manual installation this process is a bit more difficult.

First step is to remove the old installation. I figured out that it would be good to first remove all the packages installed with cabal and then remove GHC. There’s a problem though. Cabal doesn’t have uninstallation feature. This means that each package has to be manually unregistered using ghc-pkg and then all the files belonging to that package have to be removed. After spending about 30 minutes trying to figure out why I can remove one package using

ghc-pkg list | grep -v "^/" | sed -e "s/\[ {}\]//g" | head -n 1 | xargs ghc-pkg --force unregister

but can’t remove all the packages using

ghc-pkg list | grep -v "^/" | sed -e "s/\[ {}\]//g" | xargs ghc-pkg --force unregister

I gave up and decided to simply remove all of GHC files. This wasn’t easy since they were scattered all over /usr/local/``{bin,lib,share,doc}, but in the end I managed to remove everything.

I noticed that there is a lot of discussion in the community whether packages installed with cabal should go to /usr/local or to user’s home directory. Surprisingly to me it seems that most people follow the home directory approach. This approach doesn’t suit me completely. I have a separate home partition used only to store settings and email - which I’ve been told is a “complex partition setup” :-o - and all the software is kept on / partition, with all programs not installed from the packages being placed in /usr/local (BTW. it would be nice to have a separate partition for that one directory). This approach certainly wouldn’t work in a multi-user environment and I guess it could be problematic if I developed many projects, each with different dependencies (cabal-dev aims to solve that problem). As a side note, it seems to me that with hundreds of packages available from Hackage and a management tool with rather limited capabilities (cabal can’t even automatically update installed packages!) Haskell community is in a place where Linux community was over ten years ago. The dependency hell, now gone from Linux, looms over Haskell world and if cabal won’t be enhanced I see this as a very huge problem hindering large Haskell projects. It seems that Yesod team is particularly concerned about this - see here and here.

Anyway, I decided to place my new installation of the platform in /usr/local, but this time I was smarter by placing everything in a dedicated directory. Both GHC and the platform can be installed within a specific path. This is done by passing --prefix=/some/path to configure script. The only trick is that after installation of the platform ~/.cabal/config file in the /root directory has to be edited to point to the directory in which installed packages are to be placed. Of course, you have to also add the /your/haskell/platform/directory/bin to the path, so that GHC executables are visible. Now, when the new platform comes out I can simply remove the directory with the platform and install the new version. I can also easily control the disk space used by the installation. This tends to be rather huge. GHC, Platform and packages required by EclipseFP use 1,8GB of disk space. I also noticed that binaries for programs written in Haskell are rather large. The biggest one I have, buildwrapper, is over 50MB. This is caused by the inclusion of RTS (Run Time System) into the binary but I wonder what else gets included (or is the RTS that large?).

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