Nope, that's exactly the part of Control.Concurrent which is guarded with #ifdef __GLASGOW_HASKELL__, so it won't work with Hugs and nhc98.

Nevertheless, I'm sure every platform has a good way of sleeping, so my proposal is to move (u)sleep out of the unix package into the base libraries, but I'm not sure where exactly in the hierarchy it should be placed.

Somewhere under System probably, but it doesn't really fit into any of the existing modules, and adding a whole new module seems like overkill. Perhaps just adding it to System.IO is ok. Remember to make the GHC implementation use threadDelay, because System.Posix.(u?)sleep isn't thread-safe. Cheers, Simon