p05.hs

-- P05 Reverse a list.

-- Predefined function
f0 :: [a] -> [a]
f0 = reverse

-- Recursion (inefficient)
f1 :: [a] -> [a]
f1 [] = []
f1 (x:xs) = f1 xs ++ [x]

-- Tail recursion
f2 :: [a] -> [a]
f2 = f2' []
 where f2' :: [a] -> [a] -> [a]
       f2' acc [] = acc
       f2' acc (x:xs) = f2' (x:acc) xs

-- Folding
f3 :: [a] -> [a]
f3 = foldl (flip (:)) []