@mcc I was exposed to Idris a few years ago. It looked cool but TBH I'm of the "learn everything you can about one language" school, which in my case is R (24 years and counting).
But getting into microcontrollers sent me back to Forth. As far as I know there's only uLisp for functional programming on microcontrollers. Sadly, there are zero re-usable libraries for microcontrollers in Forth or uLisp; for that you need C or C++.