I maintain an academic website for myself that duplicates a lot of the material that I also put in my cv. To avoid having to maintain multiple files of the same information, and to keep things in sync, I use tex and bib files mostly, and I generate my cv in latex and use htlatex for the website.
As a project to improve my Haskell knowledge I have been thinking of generating my website with one of the haskell based static site generators. I have easily found several hakyll sites, but only a few yst, and it isn't clear to me what problem hakyll was designed to solve that wasn't being dealt with by yst. I am interested in learning what people see as the comparative advantages and disadvantages of each, and if there is any particular reason why I might want to start with one or the other given my current base of .tex and .bib files.
Disclaimer: I am the author of Hakyll.
What Hakyll gives you is an EDSL on top of pandoc, which allows you to more easily specify how different files should be processed. It is much like a specialized make on top of Pandoc. It also offers some other features which are useful for building static websites, i.e., manipulating URLS and HTML.
I think the main difference between yst and Hakyll is that Hakyll is on one side more customizable (since the configuration is just Haskell), but probably harder to get up and running as well.