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| import Data.List (foldl') | |
| import Data.Time | |
| import Data.Time.Clock.System | |
| main = do | |
| bench "stats6" stats6 [1..10000000] | |
| bench "stats5" stats5 [1..10000000] | |
| bench "stats4" stats4 [1..10000000] | |
| bench :: (Show b) => String -> ([a] -> b) -> [a] -> IO () | |
| bench name f xs = do | |
| t0 <- getSystemTime | |
| putStrLn name >> print (f xs) | |
| t1 <- getSystemTime | |
| print $ diffUTCTime (systemToUTCTime t1) (systemToUTCTime t0) | |
| -- three passes | |
| stats4 :: (Num a) => [a] -> (Int, a, a) | |
| stats4 xs = (length xs, sum xs, sum . map (\x -> x * x) $ xs) | |
| -- one pass, strict left fold | |
| stats5 :: (Num a) => [a] -> (Int, a, a) | |
| stats5 = foldl' (\(l,s,sq) x -> (l+1, s+x, sq+x*x)) (0,0,0) | |
| -- one pass, lazy right fold | |
| stats6 :: (Num a) => [a] -> (Int, a, a) | |
| stats6 = foldr (\x (l,s,sq) -> (l+1, s+x, sq+x*x)) (0,0,0) |
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