To be fair to the OP, the original claim was: "People who have prior functional programming knowledge seem to find their stride in just a few days." I would be

To be fair to the OP, the original claim was: "People who have prior functional programming knowledge seem to find their stride in just a few days." I would be somewhat surprised if someone with no prior functional programming experience could be productive in a few days in Haskell, because as you say, there are a lot of changes to how you think about programming. It's a lot easier for people with experience in a Lisp, and even easier yet for people with experience in another ML descendant. All that said, the structure of the code definitely does help a lot in lowering the bar for contributions. When Don Stewart was on the Haskell Cast [1], he mentioned that the way they use Haskell allows contributions from people who not only have no prior functional experience but who have little CS background at all past basic programming literacy. Much of the ability to do this comes from Haskell's rigorous isolation of side effects. [1]: http://www.haskellcast.com/episode/002-don-stewart-on-real-world-haskell/ http://www.haskellcast.com/episode/002-don-stewart-on-real-w... around 42:40 or so