View source for Programming performance/Lemnext Haskell

* '''Language''': Haskell
* '''Skill''': Intermediate 
* '''Time''': 20 minutes

== Code ==
<haskell>
import Data.List (partition)

main = readFile "gspc.txt" >>= \x-> 
  let ys = map (read . last . words) $ filter ((/=) '#' . head) $ lines x in
  print $ g $ foldr f ([],10000,0) ys

f a (xs,m,b) = if p b < -0.03 
  then ((m*0.1/a,a):ys,m*0.9+s,a)
  else (ys,m+s,a) where
  (ys,zs) = partition ((>) 0.06 . p . snd) xs
  s = g (zs,0,a)
  p x = (a-x)/x

g (xs,m,a) = foldl (\x (y,_)-> x+a*y) m xs
</haskell>