FLOLAC Prerequisites

hs

myFst :: (a, b) -> a
myFst (a, b) = a

myOdd :: Int -> Bool
myOdd x = odd x

qs :: Ord a => [a] -> [a]
qs []     = []
qs (x:xs) = qs ys ++ [x] ++ qs zs
  where
    ys = [ y | y <- xs, y <= x ] 
    zs = [ z | z <- xs, x < z ]

-- 3)
--   a) `Ord` is a typeclass, it defines behavior like `<`. `>=`..etc. a little bit like 
--      interface in other languages.
--   b) `++` is an operator that concates two lists on first list's end.
--   c) ys are elements which are smaller or equal to x. zs are elements that are greater than x.
--   d) qs is a quick sort function that sorts elements in ascendant order
--   e) 
qs' input = case input of
  [] -> []
  x:xs -> let less = [ y | y <- xs, y <= x ]
              greater = [ z | z <- xs, x < z ]

          in qs' less ++ [x] ++ qs' greater