On Sun, Jul 11, 2010 at 12:59 AM, Dan Doel
You're using GHC 6.12.x presumably?
That's right.
There are known performance problems with using abstract PrimMonads in that version (and, actually, just using IO as well).
Ah, that's a shame. I'm surprised it would be affecting IO too!
In the IO case for instance, checking the core tends to reveal lots of casting
between RealWorld and PrimState IO, despite the fact that those should be
identical.
I'd certainly noticed that the Core for the PrimMonad code was huge and almost impossible to follow for the enormous amount of casting that was taking place. The good news is that, last I checked, this isn't a problem in HEAD. The
optimizer does better there somehow. The bad news is that 6.14 isn't out yet, so you probably have to wait for a real fix.
I might revert both mwc-random and statistics back to using plain ST for now, then, as having them run slightly faster than 1% of their former speed is a bit painful :-(