Henning Sato von Rosen [EMAIL PROTECTED] schrieb am 18.12.04 18:31:11:
For each basic monad there seems to be a corresponding transformer,
e.g. 'StateT' for 'State' and so on.
To be useful every transformer has a run method of some kind. For a
hypothetical
IO transformer it would look like
What about:
runIOT :: Monad m = IOT m a - IO (m a)
Keean.
Udo Stenzel wrote:
Henning Sato von Rosen [EMAIL PROTECTED] schrieb am 18.12.04 18:31:11:
For each basic monad there seems to be a corresponding transformer,
e.g. 'StateT' for 'State' and so on.
To be useful every transformer
I thought you would get the following if you have a transformer 'M':
runM :: M IO a - IO a
to run 'M'...
Keean.
Udo Stenzel wrote:
Keean Schupke [EMAIL PROTECTED] schrieb am 20.12.04 10:25:36:
What about:
runIOT :: Monad m = IOT m a - IO (m a)
I have a gut feeling that this is
Perhaps you would care to explain this then?
class Runnable m n where
run :: m - n
class (Monad m,Monad (t m)) = MonadT t m where
up :: m a - t m a
down :: t m a - m a
instance (Monad m,MonadT t m,Monad (t m)) = Runnable (t m a) (m a)
where
run = down
Or
Udo Stenzel wrote:
Keean Schupke [EMAIL PROTECTED] schrieb am 20.12.04 14:20:54:
Perhaps you would care to explain this then?
Damn, I read a pair parens in there where there was none. The result still
stands as is: no transformer version of IO is possible.
But is that beacuse it really
On Mon, Dec 20, 2004 at 02:16:52PM +, Keean Schupke wrote:
But is that beacuse it really isn't (theoretically) possible, or just
not possible
to write in Haskell (because it would involve new primitives)?
Surely if IO is (ST RealWorld a) then (StateT RealWorld m a) is more or
less the
Keean Schupke [EMAIL PROTECTED] schrieb am 20.12.04 15:17:14:
Surely if IO is (ST RealWorld a) then (StateT RealWorld m a) is more or
less the right thing?
Not at all, since ST and StateT are completely unrelated. What signature would
runSTT have? Either it exposed the contained state (the
On Mon, Dec 20, 2004 at 02:16:52PM +, Keean Schupke wrote:
Surely if IO is (ST RealWorld a) then (StateT RealWorld m a) is more or
less the right thing?
But IO is not ST RealWorld (even if GHC pretends it is): other users
of the world are not waiting for the new world produced by your
Okay but we have:
ST s a
and:
runState :: State s a - (a,s)
runST :: (forall s . ST s a) - a-- notice no s in the return
type:
so what about:
runSTT :: (forall s . ST s m a) - m a-- no s gets out (like
with ST not State)
After all there was the proposal to merge (IO a)
Ross Paterson wrote:
On the haskell list it has almost been decided that (ST RealWorld a) and
(IO a)
_should_ merge and become the same thing.
Keean.
On Mon, Dec 20, 2004 at 02:16:52PM +, Keean Schupke wrote:
Surely if IO is (ST RealWorld a) then (StateT RealWorld m a) is more or
less
Ross Paterson wrote:
But IO is not ST RealWorld (even if GHC pretends it is): other users
of the world are not waiting for the new world produced by your Haskell
program.
They're *part* of the world. IO = State RealWorld makes sense if you
think of RealWorld as encapsulating the entire state of
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
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
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
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