Is Haskell a Good Type System?

The first professional functional programming that I did was basically what you just described. It wasn't closure, but it was coffee script. And essentially what I was doing was like sort of pretend I'm following Haskell's rules. Even though I didn't have a compiler enforcing it, I would still try to follow those rules. Closure thrives in the place where you have a lot of unknown unknowns. You don't know what data you're going to get back and so you don't want to commit to a type yet.