Well, it's also possible to interchange data between these two monads by: unsafeIOToST :: IO a -> ST s a stToIO :: ST s a -> IO a Can anyone tell the possible problems related to unsafeIOToST? ^^^^^^ -- Andre ----- Original Message ----- From: Tom Bevan To: Andre W B Furtado Cc: Haskell Cafe List Sent: Thursday, January 24, 2002 4:13 AM Subject: Re: Monad composition

Andre,

I can't work out how it should be done. The way I see it, the StateIO monad should have four functions associated with it. 1/ update - a function to update the state 2/ retrieve - a function to retrieve the state from the monad These two are inherited from the standard State monad 3/ input - make a character from stndIn available to the state transformation functions 4/ output - send the state of the monad after a certain set of transformations to stndOut

I've managed to write functions 1-3 but not 4.

Here's my work so far.I'm not really sure if this is on the right track.

Tom

On Thu, 2002-01-24 at 14:32, Andre W B Furtado wrote:

...

Hi, I have the same problem. Did anyone answered your question?

Thanks, -- Andre

----- Original Message ----- From: Tom Bevan To: Haskell Cafe List Sent: Wednesday, January 23, 2002 4:29 AM Subject: Monad composition

...

Hi all,

I'm writing a programme which requires IO actions to be interleaved

with

...

operations on a State monad. From what I can work out, this means that the IO Monad and the StateTransformation monad need to be composed into a single highr order monad. Does anyone have any references or pointers on how this should be done?

Tom

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe