RE: difference between (evaluate . runST) and stToIO
They aren't identical. runST guarantees to run a complete state thread that can't interact with any other. stToIO runs some imperative actions that might interact with other stToIO calls. You might find it helpful to read 'State in Haskell' if you havn't already done so. Simon | -Original Message- | From: Hal Daume III [mailto:[EMAIL PROTECTED]] | Sent: 06 August 2002 18:55 | To: Haskell Mailing List | Subject: difference between (evaluate . runST) and stToIO | | | I can't seem to figure out what the difference is between using | | evaluate (runST action) | | and | | stToIO action | | when in the IO monad and running something in ST...they seem | to behave identically...are they? | | If they are, why do they have different type signatures (one | is ST RealWorld a - IO a, while the other is (forall s. ST s | a) - IO a)? | | - Hal | | -- | Hal Daume III | | Computer science is no more about computers| [EMAIL PROTECTED] | than astronomy is about telescopes. -Dijkstra | www.isi.edu/~hdaume | | ___ | Haskell mailing list | [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell | ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
RE: difference between (evaluate . runST) and stToIO
I can't seem to figure out what the difference is between using evaluate (runST action) and stToIO action when in the IO monad and running something in ST...they seem to behave identically...are they? If they are, why do they have different type signatures (one is ST RealWorld a - IO a, while the other is (forall s. ST s a) - IO a)? With stToIO, you can do this: do r - stToIO newSTRef stToIO $ writeSTRef r 42 ... the types prevent you doing that with runST, but runST is safe to use in pure code whereas stToIO must be used in the IO monad. Cheers, Simon ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
