I love Haskell, but as far as GHC goes, its REPL story is awful: your environment doesn't even survive loading a new file! You can ask it to replay your bindings, but that's a pretty crappy solution, likely to produce unpredictable errors and, if you're doing any serious computation (such as when theorem proving), it's probably useless.

Compare this to a language like Ocaml, where I have worked at the exact same REPL, modifying the same environment, for months at a time.

This was such a standard thing to do in the Lisp and ML worlds that these languages traditionally include a save-lisp-and-die function which saves your entire runtime to disk so it can be reloaded later. (We used DMTCP in Ocaml for the same effect).

Not to moan too much. Haskell is still my favourite language. I just wish it had a decent REPL.