each f []     = return ()
each f (x:xs) = do 
  f x
  each f xs

mapp f []     = []
mapp f (x:xs) = f x : mapp f xs

filt f []     = []
filt f (x:xs)
  | f x       = x : filt f xs
  | otherwise = filt f xs
  
redu f i []     = i 
redu f i (x:xs) = do 
  let a = f i x 
  redu f a xs
  
main = do
  putStrLn "Hello, World!"
  print $ mapp (*2) [1..5]
  print $ filt odd  [1..10]
  print $ redu (\a c -> a * c) 1 [1..5]
  each print [1..5]