@rae: Type-checker plugins

Richard Eisenberg explains what GHC type-checker plugins do and demonstrates how to build a basic one.

This video walks through what a type-checker plugin does and demonstrates a very basic one. Toward the beginning of the video, I say that I use HEAD GHC instead of a released version, but then I never returned to say why. I had several technical glitches unrelated to Haskell while recording (cleverly edited out), and I lost this particular thread in my head. The reason HEAD is necessary is because my first attempt at the plugin failed, due to complications around flattening. Luckily, work I did in GHC this past winter removed the flattener (as a preliminary step to removing derived constraints), and so the solution to my problem was just to use HEAD. :) Code from the video: github.com/goldfirere/video-resources/tree/main/2021-06-01-p… Matthew Pickering's excellent collection of links on the subject: mpickering.github.io/plugins.html Find me at richarde.dev/ or on Twitter at @RaeHaskell.