plp/haskell/haskell4.hs

lenght :: [a] -> Integer
lenght [] = 0
lenght (x:xs) = 1 + lenght xs

data Tree a = Leaf a | Branch (Tree a) (Tree a)
aTree = Branch (Leaf 'a') (Branch (Leaf 'b') (Leaf 'c'))

ones = 1 : ones
numsFrom n = n : numsFrom (n + 1)

fib = 1 : 1 : [a + b | (a, b) <- zip fib (tail fib)]

data TrafficLight = Red | Yellow | Green

instance Eq TrafficLight where
    Red == Red = True
    Yellow == Yellow = True
    Green == Green = True
    _ == _ = False

instance Show TrafficLight where
    show Red = "The color of the semaphore is Red"
    show Yellow = "The color of the semaphore is Yellow"
    show Green = "The color of the semaphore is Green"

data CMaybe a = CNothing | CJust Int a deriving (Show)

instance Functor CMaybe where
    fmap f CNothing = CNothing
    fmap f (CJust counter x) = CJust (counter+1) (f x)

applyMaybe :: Maybe a -> (a -> Maybe b) ->  Maybe b
applyMaybe Nothing _ = Nothing
applyMaybe (Just x) f = f x

data Clist a = CNode a (Clist a) | CEnd (Clist a)
instance (Eq a) => Eq (Clist a) where
    CEnd _ == CEnd _ = True
    (CNode a next) == (CNode b next2) = (a==b) && next == next2
    _ == _ = False

clist2list :: Clist a -> [a]
clist2list (CEnd end) = []
clist2list (CNode a next) = a : clist2list next

list2clist :: [a] -> Clist a
list2clist [] = let new = CEnd new
                in new
list2clist (x:xs) = let first = CNode x $ list2clist' xs first
                    in first

list2clist' [] first = CEnd first
list2clist' (x:xs) first = CNode x $ list2clist' xs first

cmap :: (a -> b) -> Clist a -> Clist b
cmap f (CNode x next) = let first = CNode (f x) $ cmap' f next first
                        in first
cmap' f (CEnd x) first = (CEnd first)
cmap' f (CNode x next) first = CNode (f x) $ cmap' f next first

transpose :: [[a]] -> [[a]]
transpose [] = []
transpose ls = let hs = map head ls
                   ts = filter (not . null) $ map tail ls
               in hs : transpose ts