Haskell on Windows

Recently I’ve had reason to write a few tools for Windows. Nothing complicated, and since there was nothing “mission critical” (there hardly ever is for me :-) ) I decided to try to write them in Haskell rather than Python or C/C++. This post contains some sort of recollection of my experience so far.

First off I should probably disclose that I don’t particularly like Windows. Besides feeling more at home on a Unix (Linux) system I find that Windows also upsets me on a very basic level. If I spend a whole day at work in Windows I tend to go home more stressed and irritated than after a day in Linux. Part of this is probably due to my familiarity with Linux. My hope was that the combination of the immense joy of programming Haskell and my loath of the Windows platform I would end up with something that at least was bearable. It turns out I did.

My setup

Besides installing the pre-built GHC I also installed Visual Studio Express more later to explain the need for it. I don’t like the Visual Studio environment so I installed CMake and jEditi. Last but not least I installed Console, it addresses the fact that Windows’ “DOS-box” is an amazing piece of crap.

FFI on Windows

First, GHC comes with a number of Windows-specific modules and they cover an impressive number of the Win32 API functions. The Win32 API is simply huge and one will sooner or later come find the need to add to what those modules offer. Second, GHC is able to compile C code by delegation to MinGW, however MinGW doesn’t completely cover the Win32 API either and if one is unlucky MinGW isn’t enough for the task at hand. Of course that’s exactly what happened to me. So, I installed Visual Studio Express, but since I don’t like VS that much and I didn’t want VS solutions in my darcs repository I decided to use CMake to build a library that I then instruct GHC, through a Cabal file, to link with my Haskell code. The end result is that building requires a few extra steps before the familiar configure/build sequence. It works remarkably well really, and I’ll definately use that strategy again if I need to.

There is a benign warning thrown when linking the final executable though:

Warning: .drectve `/manifestdependency:"type='win32' name='Microsoft.VC90.CRT'
version='9.0.21022.8' processorArchitecture='x86' publicKeyToken='1fc8b3b9a1e18e3b'"
/DEFAULTLIB:"uuid.lib" /DEFAULTLIB:"uuid.lib" /DEFAULTLIB:"MSVCRT" /DEFAULTLIB:"OLDNAMES" '
unrecognized

It seems that it might be possible to skip the extra steps in the future if Cabal ticket #229 is addressed.

Windows System modules

Admittedly I haven’t been using much of the functionality in these modules, but it happens that the only function I needed had a bug that results in a segmentation fault, sometimes. See GHC ticket #2097 for some details. I guess this confirms my impression of most Haskell hackers being Linux/BSD/Unix users.

Conclusions

I won’t drop Haskell on Linux anytime soon, but I’ve found Haskell on Windows to be possible. As I suspected when I started out, Haskell does make Windows somewhat easier to bear.

  1. ordinarily I would install Vim but I thought I’d try out another editor. Vim on Windows is somewhat “leaky”, i.e. it sometimes shows behaviour that betrays its Unix roots.[back]
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