On Dec 3, 2007 3:54 PM, Ben Franksen
I don't buy this. As has been noted by others before, IO is a very special case, in that it can't be defined in Haskell itself, and there is no evaluation function runIO :: IO a -> a.
I'm not sure what a function of type m a -> a has to do with the concept of a monad. And I don't really see what the problem is with the IO monad not being definable in (pure) Haskell. IO exposes the same interface as every other Monad, and you need to use that interface to get visible results. So people have to learn it whatever. And the whole point of the Monad is that it's an interface, not a specific implementation.
I'd rather use a simple example like Maybe (modeling failure as an effect).
And I'd like to see more people getting off the ground doing interesting stuff with Haskell before their attention spans for pointless-seeming new stuff run out. I'm not talking about the smartest people in computer science courses here. I'm talking about the millions of people writing everyday Python and Ruby scripts, say, who might benefit from a more expressive, type-safe, well-thought out, fast and compiled language. -- Dan