module Example5 where

data AType = Ctr1 Int Int
           | Ctr2 Char Int Int
           | Ctr3 (Char, Int) [Char]
           deriving (Show, Eq, Ord)

foo (Ctr1 x y)       = x + y
foo (Ctr2 _ x y)     = x + y
foo (Ctr3 (_, x) xs) = x + length xs

------------------------------------------------------------------------------
-- Some predefined types

-- data Either a b = Left a | Right b

-- data Maybe a = Nothing | Just a

-- data [a] = [] | a : [a]	-- But this is not quite legal Haskell.

my_map :: (a -> b) -> [a] -> [b]
my_map f []     = []
my_map f (x : xs) = f x : my_map f xs


-- Aside: Mutual reursion.
strangeMap :: (a -> b) -> (a -> b) -> [a] -> [b] 
strangeMap f g []       = []
strangeMap f g (x : xs) = f x : strangeMap' f g xs

strangeMap' :: (a -> b) -> (a -> b) -> [a] -> [b] 
strangeMap' f g []       = []
strangeMap' f g (x : xs) = g x : strangeMap f g xs


-- Another way (note how f & g scope over the local defs.):
strangeMap2 :: (a -> b) -> (a -> b) -> [a] -> [b]
strangeMap2 f g xs = smHlp xs
    where
	smHlp []     = []
        smHlp (x:xs) = f x : smHlp' xs

	smHlp' []     = []
        smHlp' (x:xs) = g x : smHlp xs

------------------------------------------------------------------------------
-- Tree type.

data Tree a = Leaf a | (Tree a) :^: (Tree a)

sumTree (Leaf x)   = x
sumTree (l :^: r) = sumTree l + sumTree r