I remember a promising study about Haskell as a first language several years ago. The much bigger problem is indeed documentation and building a curriculum for beginners than anything about the language itself (currying included -- without background from another language you aren't already stuck in the mental state of "every function is uncurried").

Haskell is my favourite language and I like LYAH but at the end of the day OCaml infrastructure for beginners is just better. LearnOCaml in particular. It's a worse language but I get to focus on the "paradigms" part of my course without having to spend extra time teaching how to jump through Haskell's hoops. (They're good hoops, but if I covered them quickly, students wouldn't see it that way, I think.)

If we could get LearnHaskell or something and have it as easy to write exercises and configure, I'd seriously consider switching.