takeR

takeR.hs

import Test.QuickCheck

takeR :: Int -> [a] -> [a]
takeR n _ | n <= 0 = []
takeR n l | otherwise = go (drop n l) l
                        where go [] y = y
                              go (_:xs) (_:ys) = go xs ys

prop_length s n = (length s >= n && n >= 0) ==> length (takeR n s) == n
  where types = (s :: [Char], n :: Int )

prop_full s n = (length s == n) ==> (takeR n s) == s
  where types = (s :: [Char], n :: Int )

prop_empty s n = (n <= 0) ==> (takeR n s) == []
  where types = (s :: [Char], n :: Int )

prop_isomorph s n = reverse (take n (reverse s)) == takeR n s
  where types = (s :: [Char], n :: Int )

main = do
  quickCheck prop_empty
  quickCheck prop_full
  quickCheck prop_isomorph
  quickCheck prop_length