[Haskell-cafe] Re: do
Jules Bean
jules at jellybean.co.uk
Tue Dec 4 06:39:51 EST 2007
Ben Franksen wrote:
> 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.
This is a straw man. Most monads will not have such a function:
There is no function (State s a) -> a.
There is no function (r -> a) -> a.
There is no function (Random a) -> a. [assuming some random monad, often
discussed]
There is no function (Supply s a) -> a. [Another useful monad although
not one of the standard ones]
There are no (total) functions Maybe a -> a, [a] -> a, Either e a -> a.
As to the topic of the thread: I agree IO is an unusual monad. I'm not
sure if I agree that it shouldn't be used as a teaching basis. I think
there are all kinds of ways to teach haskell; I'd be inclined to want to
start with some IO, without explaining the plumbing in detail, and then
come back to it later with better perspective when discussing general
monads.
Jules
More information about the Haskell-Cafe
mailing list