[Haskell-cafe] better way to do this?

Eugene Kirpichov ekirpichov at gmail.com
Wed Oct 7 05:32:49 EDT 2009

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 <ketil at malde.org>:
> Peter Verswyvelen <bugfact at gmail.com> 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
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Eugene Kirpichov
Web IR developer, market.yandex.ru

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