Installing GHC on openSUSE Linux

The first thing you do when starting out with a new programming language is of course installing a compiler and an IDE. Although this first step should be easy, it took me a lot of work to get Haskell running on my openSUSE Linux. The solution to my problems turned out to be obvious, as all solutions are when you already know them. Nevertheless, 5 hours of my life went to waste and all I can hope for right know is saving others from repeating my mistakes.

There are two main Haskell compilers: GHC (Glasgow Haskell Compiler) and Hugs. I decided to use GHC, as it seems to be the more popular one. As a Linux user you have three options of installing GHC:

  1. Use the package repository
  2. Install precompiled binaries
  3. Compile from source

The third option is not really a sane option – GHC is written in Haskell so you would need working Haskell compiler to compile it. The first option seems to be the most natural for Linux user. Don’t we like to have our software managed from one central package management application? Good news: there is Haskell repository for openSUSE. However, after I installed GHC and some libraries from this repo it turned out the the compiler doesn’t recognize the libraries. Solution: for each library install both the normal and the devel package. Obvious, isn’t it? Well, it wasn’t obvious to me at first and I still think it’s a bit tricky. You install the compiler (which means that you most likely want to compile programs), YaST resolves the dependencies by installing additional GHC libraries, but compiler doesn’t have access to these libraries (since devel packages were not installed) and in the end GHC is totally useless. Where’s the logic?

There is one more catch with the repo. Haskell community offers a web repository of additional Haskell packages called Hackage. Not every package available via Hackage is also available in the openSUSE repository. Most notably Leksah, the Haskell IDE, is not available. So what now? Luckily with Haskell comes Cabal (Common Architecture for Building Applications and Libraries). Cabal is a package manager that manages packages available to GHC. It resolves package dependencies, downloads packages from the web, compiles and installs them. This however leads you to mixing two ways of managing GHC libraries. Some libraries will be managed by Cabal and some by YaST (or other rpm/deb management tool if you’re using different brand of Linux). This, at some point, may cause problems which leads us to the last of three installation option: using precompiled binaries. If you choose this option, carefully to chose which GHC version to download. The most obvious choice is using the latest available version, right? Wrong! You see, there is a thing called The Haskell Platform, which is a set of basic Haskell libraries required for development. New versions of Haskell Platform are released twice a year and each version is compatible with a particular version of GHC (most likely not the latest one). At this moment the latest version of GHC is 7.4.1, but the latest Haskell Platform supports GHC 7.0.4. If you’re a newbie, just like me, it is very reasonable to set up your basic Haskell environment by installing the Haskell Platform.

So, my advice on installing GHC on openSUSE (and other Linux distros) is: don’t use the repo, use the precompiled binaries. Instead, get the Haskell Platform, get the supported GHC version, install GHC, install Platform and then fell free to use Cabal to install any additional libraries from Hackage.

UPDATE (06/06/2012): The installation method described above can be enhanced. Read this follow-up for more information.

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