Hello Alberto, Tuesday, June 3, 2008, 12:56:50 PM, you wrote:
Good! So you can easily "hide" the IO operations in the ST monad. I will definitely look into it.
from implementation POV ST monad is nothing but renamed IO monad which exports only subset of its operations which are guaranteed to safe. or, saying in other words, it's just type hackery around IO monad that provides safe operations it's possible to define ST monad and its operations as following: newtype ST s a = forall s. ST_Constructor (IO a) unsafeIOtoSt action = ST_Constructor action runST (ST_Constructor action) = unsafePerformIO action newtype STRef s a = forall s. STRef (IORef a) readSTRef (STRef ref) = unsafeIOtoSt (readIORef ref) and so on. GHC uses technically (but not ideologically!) different implementation where both monads are specializations of one generic type. while Hugs afair uses exactly this approach. you may also look at ArrayRef lib which reimplements arrays/refs for both compilers in more unified way anyway, because ST is just IO monad modulo type tricks, you can execute any IO action inside ST by lifting it with unsafeIOtoSt -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com