[Haskell] IO == ST RealWorld
ross at soi.city.ac.uk
Tue Jan 24 04:40:00 EST 2006
On Mon, Jan 23, 2006 at 09:55:39PM +0100, Twan van Laarhoven wrote:
> Is there any reason why IO should not be defined as:
> > type IO a = ST RealWorld a
> in implementations that support ST?
> This way IORef/STRef and IOArray/STArray can be merged. I know under the
> hood they already share code, but this way they can also share an interface.
But IO isn't a state monad: others are concurrently changing the world
without waiting for my Haskell program to terminate. Some compilers
use a state monad to enforce sequencing, but a continuation monad or
resumption monad would work just as well.
However IO does include a state monad, so one could define (using
IORegion instead of the presumptuous RealWorld):
type IORef = STRef IORegion
type IOArray = STArray IORegion
type IOUArray = STUArray IORegion
newIORef = stToIO . newSTRef
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