Why aren't Haskell, Go and Rust on this site?

Question

see above

Answer 1

Go and Rust are relatively young language, so it is normal that they are not offered. The languages that have been added to Sololearn's lessons have been, up to now, those that have a great demand from the community. On the other hand, to offer a complete course on a topic you have to handle it, and perhaps not all the people in charge of it have a broad knowledge of the subject (especially Rust, which seems to have a somewhat elevated learning curve)

Haskell is less common. And before creating a course about it, I think it is more convenient to create an introductory one to the functional programming and its concepts.