This blog got created some years ago but has never been really maintained (Mostly because of a lack of time). Nonetheless I recently decided to document what I work and learn about and to use this blog for that.
Aside from that, I recently became one of John De Goes patreon, and attended a first training session about GADTs. The Spartan tier is $300/month which may be considered as a significant price at first, but trust me it is worth every penny. It provides you with an access to all the public trainings John gives, along with extra trainings, and monthly 1-to-1 sessions among others. If you want to boost your Functional Programming skills, this may be a good way to do it.