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Hakyll: static website generator in Haskell

by Gregor Uhlenheuer on December 1, 2011

As part of my latest interest in Haskell and functional programming in general I went ahead and switched my static website generator to Hakyll that is being written in Haskell. Before I was using rstblog which is written in Python 1.


Hakyll is a Haskell library for generating static sites, mostly aimed at small-to-medium sites and personal blogs. It is written in a very configurable way and uses an xmonad-like DSL2 for configuration.

Given the fact that Hakyll uses pandoc to parse and build the web pages Hakyll can process Markdown, reStructuredText or other popular text formats. I tried to use reStructuredText with pandoc at first so I could reuse my already written posts. Sadly that did not work out too good because I didn’t get syntax-highlighting to work properly.

Luckily converting to Markdown solved that problem and the conversion of my posts from reStructuredText wasn’t too complicated.


I am no export on Haskell yet at all so my current configuration is a pretty basic one and consists of approximately 90% of the example configurations on the Hakyll website. So it took some time to get comfortable with the Hakyll DSL and the way it is supposed to be configured.

This is the way the blog posts are rendered:

-- Posts
match "posts/*" $ do
    route $ setExtension "html"
    compile $ pageCompiler
        >>> arr (renderDateField "date" "%B %e, %Y" "Date unknown")
        >>> arr (renderDateField "shortdate" "%Y-%m-%d" "Date unknown")
        >>> renderTagsField "posttags" (fromCapture "tags/*")
        >>> applyTemplateCompiler "templates/post.html"
        >>> applyTemplateCompiler "templates/default.html"
        >>> relativizeUrlsCompiler

The following snippet illustrates the way the tag cloud is processed (though I am not really happy with the output yet):

match "tags.html" $ route idRoute
create "tags.html" $ constA mempty
    >>> arr (setField "title" "tag cloud")
    >>> requireA "tags" (setFieldA "tagcloud" (renderTagCloud'))
    >>> applyTemplateCompiler "templates/tagcloud.html"
    >>> applyTemplateCompiler "templates/default.html"
    >>> relativizeUrlsCompiler

-- ...
-- ...
-- ...

    tagIdentifier :: String -> Identifier (Page String)
    tagIdentifier = fromCapture "tags/*"

    renderTagCloud' :: Compiler (Tags String) String
    renderTagCloud' = renderTagCloud tagIdentifier 100 120


Overall I am pretty happy with the result so far. The blog looks nearly the same as it looked before - anyways there is room for a lot of improvements. These are a few points I would like to add in the near future:

So I guess the amount of spare time and my progress of learning Haskell will influece when that will happen. If you have got critique or comments of any other kind feel free to send me an .

  1. see my post on rstblog

  2. Domain Specific Language

This post is tagged with programming, haskell and web