ch5.hs

qsort [] = []
qsort (x:xs) = smaller ++ [x] ++ larger 
  where
    smaller = qsort . filter (<=x) $ xs
    larger  = qsort . filter (>x) $ xs

reverse' [] = []
reverse' (x:xs) = reverse xs ++ [x]

reverse2 xs = foldr (\x acc -> x : acc) [] xs
reverse2 xs = foldr (\x acc -> acc ++ [x]) [] xs

foldl (flip (:)) [] [1..4]
reverse2 xs = foldl (\acc x -> x : acc) [] xs

sumAll xs = foldl (+) 0 xs

scanl (flip (:)) [] [3,2,1]  

map (negate . sum . tail) [[1..5],[3..6],[1..7]]

take 10 . map ((^2) . (+3)) [1..100]
let mut x = take x . map ((^2) . (+3))
let tenth = mut 10

takes xs = take 10 . map ((^2) . (+3)) $ xs