On Sat, Aug 14, 2010 at 10:11 PM, Bill Atkins <watkins@alum.rpi.edu> wrote:
On Saturday Aug 14, 2010, at 12:50 AM, Conal Elliott wrote:

> And the IO monad is what Jerzy asked about.  I'm pointing out that the state monad does not capture concurrency, and the "EDSL model" does not capture FFI.  (Really, it depends which "EDSL model".  I haven't seen one that can capture FFI.  And maybe not concurrency either.)
>

So which model captures the way the IO monad works?

I don't think anyone has given a denotational (functional-style) model for the meaning of IO.  As I wrote elsewhere:

IO carries the collective sins of our tribe, as the scapegoat did among the ancient Hebrews. Or, as Simon Peyton Jones expressed it, “The IO monad has become Haskell’s sin-bin. Whenever we don’t understand something, we toss it in the IO monad.” (From Wearing the hair shirt – A retrospective on Haskell.) Is it likely that we can then come along later and give a compelling and mathematically well-behaved notion of equality to our toxic waste pile? Or will it insist on behaving anti-sociably, as our own home-grown Toxic Avenger?