Go to part 1 of this series

There’s no code today. Just lots and lots of words. Code will follow soon!

Both Yesod and Hakyll are well-documented and have reasonable tutorials: both Michael Snoyman’s book and Jasper Van der Jeugt’s site are great resources.

Template system mismatches

What is not documented is how to combine the two. Part 1 of this series describes my Apache configuration for serving content from the two parts of the web site. After figuring that out, the most difficult challenge was making the two parts of the sites look and feel as if they were part of a single coherent site. The single biggest complexity is that both frameworks employ different templating systems by default. Yesod employs Shakespearean templates, specifically Hamlet, Lucius and Cassius. Hakyll has its own straightforward, but effective, system. I enumerate some of the interesting characteristics below:

• Shakespearean templates
  • Strongly-typed templates that are parsed at compile time
  • Dynamic “runtime” variants of the templates are supported, but are decidedly “second-class” compared to the strongly-typed variants as one might expect given that Yesod’s strong emphasis on type safety
  • Hamlet (the HTML templates) use a Haml-based syntax
• Hakyll templates
  • HTML-based
  • Fully dynamic much more like the kinds of templates that non-Haskell developers are typically used to

Philosophical thoughts

Both systems have their pros and cons. However, on a personal note, I have a soft spot for Hamlet’s syntax. However, I don’t object to using real HTML. Ultimately, the question came down to the following: do I adapt my Yesod app to consume Hakyll templates or do I adapt my Hakyll site generator to handle the templates from my Yesod app. Given my unwillingness to compromise the type safety of my Yesod app, I decided to do the latter.

Possible approaches

There were three main approaches I considered:

• Add an “empty” page to my Yesod app whose sole purpose is to serve up its default layout template rendered as HTML containing Hakyll-style placeholders: in this model, I’d run a local Yesod development instance while running my Hakyll generator: the Hakyll generator would pull its default layout template from the Yesod app using the Haskell equivalent of wget and then use that to render the static site
• Add Hamlet support directly to my Hakyll site generator

I toyed with the first approach briefly and then decided that this was not personally very satisfying. Both Yesod and Hakyll are highly modular and configurable frameworks, so I decided to power through things and simply use the shakespeare in my Hakyll app.

As I’ll describe in future instalments of this series, this was not entirely straightforward, but did ultimately result in a reasonably elegant solution to the problem.

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