On 12/22/05, John Meacham
Just the idea that you can write things like mapM and replicateM is enough to blow the mind of many impertive programmers.
Not trying to fan the flames, but one thing I struggle with is understanding (at a "gut level" - if you explain the theory, I'll understand, but go away none the wiser in practice...) why I need mapM as well as map (and all the other -M functions, liftM, foldM, etc...) mapM and so on really *are* why the IO monad is a great feature of Haskell. But the mental gearchange needed to appreciate what just happened is one of the speedbumps on the learning curve. You thought you were getting along fine, you'd got the point of functional stuff like map and fold, and you understood IO and it wasn't as scary as you'd thought. But then along comes mapM, and you're struggling again - why not just use map? And the explanation doesn't help much, it just leaves you feeling that you'd missed the point. As I say, I'm not trying to criticize anyone here, but it seems to be quite hard to get across to people who have understood and assimilated this sort of stuff, just how hard it feels to newcomers. We understand the explanations (we do! really! :-)) but even understanding them, we are still left with a lack of confidence. It's like being shown a full set of carpentry tools, having every one explained, but still reaching for the hammer every time and banging something no matter what we're trying to do :-) Paul.