Re: ST and IO. Two problems. Some old some new?

On Thu, Feb 07, 2002 at 12:41:50PM +0100, Koen Claessen wrote:

Amr Sabry wrote: | 2. Soundness of stToIO : | data Var a = Var { get :: () -> IO a, | set :: a -> IO ()}

(Why does get have this type?)

[...]

The type of stToIO is:

stToIO :: ST RealWorld a -> IO a

This was discussed in glasgow-haskell-bugs in Oct 2000. GHC does indeed use a sound type, but it is documented as the unsound StTOIO :: ST s a -> IO a and that is the type that Hugs uses. (Call it IORegion instead of RealWorld if you like.)