In the long term, I have been considering rewriting ikiwiki in haskell. It's appealing for a lot of reasons, including:

• No need to depend on a C compiler and have wrappers. Instead, ikiwiki binaries could be built on demand to do the things wrappers are used for now (cgi, post-commit, etc).
• Potentially much faster. One problem with the now very modular ikiwiki is that it has to load up dozens of perl modules each time it runs, which means both opening lots of files and evaluating them. A haskell version could run from one pre-compiled file. Other speed efficienies are also likely with haskell. For example, pandoc is apparently an order of magnitude faster than perl markdown implementations.
• Many plugins could be written in pure functional code, with no side effects. Not all of them, of course.
• It should be much easier to get ikiwiki to support parallel compilation on multi-core systems using haskell.

• A rewrite would be an opportunity to utterly break compatability and redo things based on experience. Since the haskell libraries used for markdown, templates, etc, are unlikely to be very compatable with the perl versions, and since perl plugins obviously wouldn't work, and perl setup files wouldn't be practical to keep, a lot of things would unavoidably change, and at that point changinge everything else I can think of probably wouldn't hurt (much).

  • Re templates, it would be nice to have a template library that doesn't use html-ish templating tags, since those are hard for users to edit in html editors currently.
  • This would be a chance to make WikiLinks with link texts read "the right way round" (ie, vaguely wiki creole compatably). [See also link plugin perhaps too general? --smcv]
  • The data structures would probably be quite different.
  • I might want to drop a lot of the command-line flags, either requiring a setup file be used for those things, or leaving the general-purpose --set var=value flag.
  • Sometimes the current behavior of --setup seems confusing; it might only cause a setup file to be read, and not force rebuild mode.
  • Hard to say how the very high level plugin interface design would change, but at the least some of the names of hooks could stand a rename, and their parameter passing cleaned up.

We know that a big, break-the-world rewrite like this can be a very bad thing for a project to attempt. It would be possible to support external plugins written in haskell today, without any rewrite; and a few of the benefits could be obtained by, eg, making the mdwn plugin be a haskell program that uses pandoc. I doubt that wouod be a good first step to converting ikiwiki to haskell, because such a program would have very different data structures and intercommuniucation than a pure haskell version.

Some other things to be scared about:

• By picking perl, I made a lot of people annoyed (and probably turned several people away from using ikiwiki). But over time there turned out to be a lot of folks who knew perl already (even if rustily), and made some very useful contributions. I doubt there's as large a pool of haskell programmers, and it's probably harder for a python user to learn haskell than perl if they want to contribute to ikiwiki.
• It might be harder for users of hosting services to install a haskell based ikiwiki than the perl version. Such systems probably don't have ghc and a bunch of haskell libraries. OTOH, it might be possible to build a static binary at home and upload it, thus avoiding a messy installation procedure entirely. --Joey