"Pipes" in Haskell

pipes.hs

#!/usr/bin/env runhaskell

-- Single and double pipe operators are taken, so use triple-pipe :)
infixl 9 |||
(|||) ::  a -> (a -> b) -> b
x ||| f = f x


len = fromIntegral . length 
mean xs = sum xs / len xs

stddev1 xs = xs ||| map (subtract my) ||| map (^2) ||| sum ||| (/n) ||| sqrt
	where	my = mean xs;
		n = len xs 

stddev2 xs = sqrt $ (/n) $ sum $ map (^2) $ map (subtract my) $ xs  -- Two maps in succession can be combined: map ((^2).subtract (mean xs))
	where	my = mean xs;
		n = len xs 

datapoints = [2,4,4,4,5,5,7,9]
my = mean datapoints
sigma = stddev1 datapoints

main = print (sigma)