haskell is great if you enjoy learning haskell. there's always a new build system, a complete redesign of how things are done, etc. i lost the plot around the time everything became an arrow (or was it a lens ?) myself, but I'm sure a few more generations of improvement have happened already!
it just seemed like the tutorials just pivoted from monads to lenses to arrows. but fair enough, I never did "get" haskell. I loved the functional aspect of functional problems (e.g science equations), but once it came to carrying state, everything just turned into a mess for me.
But yeah, I guess C++ is the one single language where you can keep learning more and more fundamental things, forever.