Gosh, thank you everybody! Let me try to summarise where I am, given all the help. haskell-cafe is an okay place to ask this stuff. (-: I should also check out the wiki too; it looked a bit scary to use last time I looked, but it seems to have relevant stuff. It's a pity that the mailing list archives aren't more easily searched; maybe applying google to them would work. Part of my confusion was due to a usual problem with teaching. People come in to a lesson with preconceived ideas X, the teacher tells them stuff Y, and instead of coming out of the lesson thinking Y, they come out thinking f(X,Y), because the teacher didn't tell them not-X. It's instructional to ask children where they think trees' mass comes from as they grow, after a lesson on the subject. I originally thought that "IO a" meant "an a whose value may depend on some IO that was done", as if that data were tainted by other data it touched which stemmed from IO actions. Instead, "IO a" it appears to mean "some IO action you can do that will give an a", and you can only do stuff with the "a" within an "IO-aware" context. A Haskell program is an IO action. I got the idea of tainted data from Perl, which is a security aid to help you ensure that any data drawn from outside your program has to be approved by you before your program can use it to affect other things outside your program. Try to keep most code functional, even if this means that your monadic code uses very complex referentially-transparent helper functions. I hadn't bumped into Theo Norvell's monad tutorial yet. I'm guessing that it's the one at http://www.engr.mun.ca/~theo/Misc/haskell_and_monads.htm ? I'll take a look. There is a concept of being in the IO monad. My current concept of "A >>= B" is that it helps let B into the monad that A's in. This is how 'head' is let in by readFile "/etc/hosts" >>= (return . head) I find fmap deeply strange, though, because I don't really understand functors. People pointed me towards fmap, and I figured from IO's instance of Functor that fmap head $ readFile "/etc/hosts" also works, so I plan to learn a little category theory to help find out why this makes sense. (Someone also taught me how to use $. (-:)
= actually has the type (Monad m) => m a -> (a -> m b) -> m b That makes some sense.
I get >> and the syntactic sugar of 'do' looks fairly simple so I'll probably start using that more once I'm happy with the translation between that and >>= All the best, Mark