On Tue, May 11, 2010 at 8:28 PM, wren ng thornton <w...@freegeek.org> wrote: > Max Cantor wrote: >> >> Based on some discussions in #haskell, it seemed to be a consensus >> that using a modified continuation monad for Error handling instead >> of Eithers would be a significant optimization since it would >> eliminate a lot of conditional branching (everytime >>= is called >> in the Either monad, there is a conditional. >> I implemented a ErrCPS monad which does exactly that, but the speed >> has been disappointing. It runs almost exactly 3x slower than a >> drop in replacement using the MonadError instance of Either from mtl. > > > I have noticed speedup in my CPS version of Maybe[1] (kidnapped from the > Wiki) so the difference is curious. Jan-Willem's comments about closures are > significant when doing CPS work, but I'd expect Maybe and Either to perform > similarly, whatever their performance is. It's been a while since I've > benchmarked MaybeCPS, so perhaps I now have the slowdown too. Let's look at > the code and see if we can find other differences... > > [1] > http://community.haskell.org/~wren/wren-extras/src/Control/Monad/MaybeCPS.hs > > > Here's one big difference: > >>> newtype ErrCPS e m a = ErrCPS { runErrCPS :: >>> forall r . (e -> m r) -- error handler >>> -> (a -> m r) -- success handler >>> -> m r } > > The analogous version I use is: > > newtype MaybeCPS a = MaybeCPS > (forall r. (a -> Maybe r) -> Maybe r) > > While I also offer a transformer version of MaybeCPS, the transformer *does* > suffer from significant slowdown. Also, for MaybeCPS it's better to leave > the handlers inline in client code rather than to abstract them out; that > helps to keep things concrete. So perhaps you should first try a direct CPS > translation: >
Is the CPS transformed MaybeT slower because it's done in 2-CPS, rather than in 1-CPS like the MaybeCPS? I only did MaybeT in 2-CPS because it was the easiest, not because I thought it would be easiest. Antoine _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
