Re: [Haskell-cafe] better way to do this?

It's a complex area not a lot of people are working in. Similar (actually worse than) dependent typing. Regards, John A. De Goes N-Brain, Inc. The Evolution of Collaboration http://www.n-brain.net | 877-376-2724 x 101 On Oct 7, 2009, at 3:32 AM, Eugene Kirpichov wrote:

Or you can use an effect system (however that doesn't give you the opportunity of overriding IO functions, but I think that providing such an opportunity with the means you suggest (splitting IO into many sub-monads) is not going to be usable in the large scale)

By the way, I am surprised that there seems to not exist any non-purely-academic language at all that supports effect systems! (except for Java's checked exceptions being a poor analogue). The only language with an effect system *and* a compiler that I know of is DDC, but it seems to be purely experimental.

2009/10/7 Ketil Malde :

...

Peter Verswyvelen writes:

...

So yes, without using IO, Haskell forces you into this safe spot

One could argue that IO should be broken down into a set of "sub- monads" encapsulating various subsets of the functionality - file system, network access, randomness, and so on. This could extend the "safe spot" to cover much more computational real estate, and effectively sandbox programs in various ways.

So instead of 'main :: IO ()', a text processing program using stdin and stdout could have type 'main :: MonadStdIO m => m ()'. For testing, you could then define your own monad implementing 'putStrLn' and 'readLn' etc, and a function 'runStdIO :: MonadStdIO m => m () -> String' that you are free to use in your quickcheck properties.

(ObAttribution: I think it was a posting by Lennart Augustsson on unique names that brought this to my mind, but a quick googling didn't find that exact mail.)

-k -- If I haven't seen further, it is by standing in the footprints of giants _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- Eugene Kirpichov Web IR developer, market.yandex.ru _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe