Haskell: ok to recursively call main?

It's perfectly fine, but it's pretty uncommon that every part of your program is repeated indefinitely. Usually you have some one-time setup or something, and then you enter into a loop to execute the remainder; or you have some cleanup to do after the main loop finishes. In that case you can't call main again, because it would do the one-time setup (or cleanup) every time. If you have no one-time setup, feel free to have main call itself.

Since last call optimizations are a regular thing in Haskell, yes, that's completely fine. Learn You A Haskell includes some examples using this kind of recursion. Also, this StackOverflow's post digs a little deeper in this topic.