Felipe Lessa
Very interesting! And the API seems very nice, although I haven't used the package.
Are there benchmarks for monad transformers? How big is the difference between CPS and non-CPS monad libraries?
I have run some small and probably not that meaningful benchmarks. For StateT it doesn't seem to make a lot of difference. ChoiceT appears to be considerably faster than [] in all tests I've made. As a small benchmark consider the following factoring functions, which return a (very redundant) list of factors of the argument: testComp1 :: Integral a => a -> [a] testComp1 n = do x <- [1..n] y <- [x+1..n] guard $ n - x /= y guard $ mod (x^2 - y^2) n == 0 return $ gcd n (x-y) testComp2 :: Integral a => a -> ChoiceT r i m a testComp2 n = do x <- choice [1..n] y <- choice [x+1..n] guard $ n - x /= y guard $ mod (x^2 - y^2) n == 0 return $ gcd n (x-y) On my machine testComp1 takes 5.6 seconds to finish, and testComp2 takes 3.9 seconds. The programs I've used to test are: main1, main2 :: IO () main1 = do hSetBuffering stdout (BlockBuffering Nothing) getArgs >>= mapM_ (print . testComp1 . read) main2 = do hSetBuffering stdout (BlockBuffering Nothing) getArgs >>= mapM_ (print . listChoice . testComp2 . read) To take this further I modified the benchmark to print only the first result found. To return a factor of 1237*65537 testComp1 needs 10.2 seconds, while testComp2 needs only 5.1 seconds. Here is the modified code (testComp1 and testComp2 remain unchanged): main1, main2 :: IO () main1 = getArgs >>= mapM_ (print . head . testComp1 . read) main2 = getArgs >>= mapM_ (print . maybeChoice . testComp2 . read) At least ChoiceT is faster than using regular lists, and it's also a CPS-based monad transformer, so you get all the goodies of CPS and combining monads: testComp3 :: (Integral a, Monad m, LiftBase m, Base m ~ IO) => a -> ChoiceT r i m a testComp3 n = do x <- choice [1..n] y <- choice [x+1..n] guard $ n - x /= y guard $ mod (x^2 - y^2) n == 0 let factor = gcd n (x-y) io $ printf "Factor found: %i\n" (toInteger factor) return factor Note that instead of 'listA' I'm using the 'choice' function, which is slightly faster, but even with 'listA' ChoiceT outperforms regular lists. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/