Installing pandoc on Slackware

I’ve just spent several hours getting Pandoc to work on my Slackware64 system, so I thought I would quickly document what I needed to do before I forget it.

The Glasgow Haskell Compiler

Bad news, Pandoc is written in Haskell—surely a great programming language, but a language for which there is no compiler in Slackware.

Fortunately, installing the Glasgow Haskell Compiler was quite easy, once I got past the fact that I would not be able to build it from source on my system without a Haskell compiler—but if I had a Haskell compiler on my system, then I would not try to build one… I took the binary distribution for the “x86_64-unknown-linux” platform, which happened to work fine on Slackware64-14.1 (the 7.8.2 release did not, because of a missing libtinfo library ¹).

The Haskell Platform

Then I needed to install the Haskell Platform, a collection of Haskell “packages”. It provides several packages required by Pandoc (not all, though), and more importantly it provides the cabal tool, which allows to install more packages, even though it is reportedly not a package manager—the subtlety is beyond me, but then I’m not a Haskell programmer.

Installing the Haskell Platform was more difficult, due to several problems in its build system:

• The configure script stopped after a few lines, complaining about a GHC_PACKAGE_PATH environment variable, which is “incompatible with Cabal”. Since there was no such variable in my environment, this is a bug in the build system, which has already been reported.
• Like so many software packages out there, it ignored the configure script’s --libdir option, and ended up installing the libraries in $prefix/lib even if I invoked the script with --libdir=/usr/lib64.
• It does not support staged installs! I had a hard time believing that, but this was confirmed by a bug report from two years ago (the ticket mentions that the “milestone” is set to “2013.2.0.0”, but it is definitely not fixed in that release). Please, software developers: the ability to perform “staged” install—that is, installing all files in a directory (usually empty) arbitrarily choosen by the user instead of the root hierarchy—is essential for creating proper packages. If your project does not support staged installs, then somewhere, at this very moment, a packager is cursing you.²

A small patch (inspired by the one submitted by “AlainODea”, in the above-mentioned bug report) allows to overcome these issues.

After installation, update the cache of Haskell packages by running the following command:

# ghc-pkg recache

If you forget to do that, the compiler will ignore all the packages you have just installed, and as a result, attempts to compile supplementary packages will inevitably fail due to “insatisfied dependencies”.³

Pandoc

I quickly renounced to prepare SlackBuilds for all Haskell packages required to run Pandoc, and for Pandoc itself. I chose instead to use the cabal “not-a-package-manager” tool, as recommended:

$ cabal update
$ cabal install pandoc

But I ran into a last problem: one of Pandoc’s dependencies, the temporary package (version 1.2.0.2), failed to build due to a compile-time error in System/IO/Temp.hs. Since patching Haskell code is way beyond my abilities, I ended up forcing cabal to use the previous version of the package (hoping the compile-time error was introduced in the last release, which seemed to be the case):

$ cabal install --constraint=temporary==1.2.0.1 pandoc

Then everything went fine and I got the pandoc tool I wanted from the beginning.

1. ↑ It seems that symlinking libtermcap to libtinfo is enough to allow the 7.8.2 release to work—thanks to G. Smith.
2. ↑ Most build systems, and all proper build systems—including those generated by the Autotools—can provide that feature.
3. ↑ This may sound obvious, but I actually lost one hour because of that…

7 May 2014