As far as I understand it IO is a special case of a state monad (where the state is the "World". If this is the case and there is a state-transformer (StateT) then it should be possible to write an IO transformer. Unfortunately I also think because of some magic in the ST and IO monads, you cannot write the transformer yourself, as it would require compiler support. Keean. Henning Sato von Rosen wrote:
Hi all!
For each basic monad there seems to be a corresponding transformer, e.g. 'StateT' for 'State' and so on.
I guess the reason lies in the fact that if there were an IO Transformer monad, one might run it and get the 'Universe' out of the IO monad.
But, I am working on understanding IO magic, on a much more concrete level, so I am am looking for a really good explanation of the above. (And the IO monad in general.)
Thanks!
/Henning _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe