On Thu, Oct 26, 2006 at 06:15:59PM +0100, Ross Paterson wrote:
He's already been there:
http://www.haskell.org/pipermail/haskell/2006-January/017410.html
I yes, I saw that post, but didn't read it carefully, and didn't think of it, but am sure it must have been lurking in the back of my mind suggesting that this could be done. Usually I find Oleg's solutions well nigh incomprehensible, but in this case, it seems downright simple. The only catch is that you've got to use a new monad. And I suppose there's a possibility of confusing error messages. I suppose, though, that this kind of change would best be part of a complete refactoring of the IO monad (which is something I've been longing to do--to break (almost?) all the IO functions into classes, so you could write standard IO code that can run in other monads (e.g. a tarball-reading monad, or a quickcheck fake-IO monad, or in darcs the SlurpMonad), or could use it to statically enforce constraints (e.g. this bit of IO code doesn't touch the network, doesn't write to disk, etc). Not that I expect to have time to do this any time soon, but it'd be beautiful... and we all know that physicists (and I suppose computer scientists, too?) are suckers for the beautiful. -- David Roundy Dept. of Physics Oregon State University