Enable GHCi to run commands under StateT monad based on IO or maybe even any other monad based on IO. So that you could for example exec a state and "fall" into this monad.

This could be generalized by supporting interactive "do" notation. Currently doing something like:

(flip execStateT) state $ do

raises "Empty 'do' construct" warning, but GHCi could go into interactive mode where it would be possible to write one command after another and it would execute them.