On Mon, Apr 12, 2010 at 8:53 PM, Isaac Dupree
On 04/10/10 11:35, Twan van Laarhoven wrote:
If MonadIO were in base, then the base library itself could also use it. For example the functions in System.IO could be lifted to work on any MonadIO monad. Whether that is a good idea is completely orthogonal to this discussion, however.
I think it is relevant to the discussion to consider whether the MonadIO class is a good idea in general -- if it's not a broad enough use, then maybe we shouldn't implicitly sanction it by putting it in 'base'. Is it mainly to make monad-transformer code more readable* by requiring fewer explicit lifts? Are there other reasons? (Pointing to example code that uses MonadIO would be a good answer.)
This is the code which prompted my original thread: http://hackage.haskell.org/packages/archive/starling/0.2.0/doc/html/Network-... So the answer to your question is 'polymorphism'.
*i've grown increasingly doubtful of the idea that more classes / less-explicit code reliably makes things more readable.
Perhaps true! At the time I wrote the above, I was frustrated with having to nail myself down to a particular technique of signaling/expressing errors, so I erred on the side of polymorphism.
(I see nothing wrong with splitting MonadIO out into a new package (besides that proliferation of packages is a bit annoying)... )
I would be for any approach which lets me use MonadIO without pulling in the mtl or transformers. Antoine