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
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
On Sat, 18 Dec 2004, Henning Sato von Rosen wrote:
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.)
One way of looking at it is that a monad is an interpreter that has access to a haskell interpreter (typically called by return). You can't write an IO interpreter in terms of anything else, so you can't layer it on top of something - it's got to be on the bottom of the stack. -- flippa@flippac.org A problem that's all in your head is still a problem. Brain damage is but one form of mind damage.
participants (3)
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Henning Sato von Rosen -
Keean Schupke -
Philippa Cowderoy