Xerxes solutions to typeclass problems

gistfile1.hs

data List a = Elem a | List [List a] deriving (Show)

flatten' :: List a -> [a]
flatten' (Elem x) = [x]
flatten' (List (x:xs)) = flatten' x ++ flatten' (List xs)
flatten' (List []) = []


data Tree a = Empty | Node a (Tree a) (Tree a)
               deriving (Eq, Show, Read)

treeInsert :: Ord a => Tree a -> a -> Tree a
treeInsert Empty a = Node a Empty Empty
treeInsert tree@(Node v l r) a
    | v > a  = Node v (treeInsert l a) r
    | v < a  = Node v l (treeInsert r a)
    | v == a = tree


treeFromList :: Ord a => [a] -> Tree a
--treeFromList [] = Empty
--treeFromList (x:xs) = treeInsert (treeFromList xs) x
--treeFromList xs = foldr (\x acc -> treeInsert acc x) Empty xs
--treeFromList = foldr (\x acc -> flip treeInsert x acc) Empty 
treeFromList = foldr (flip treeInsert) Empty 


class Mappable m where
    mmap :: (a -> b) -> m a -> m b

instance Mappable List where
    mmap f (Elem x) = Elem (f x)
    mmap f (List xs) = List(map (mmap f) xs)


mmap' :: (a->b) -> List a -> List b
mmap' f (Elem x) = Elem (f x)
--mmap' f (List []) = List []
--mmap' f (List (x:xs)) = List (mappedFirst : mappedRest)
--  where
--    mappedFirst = mmap' f x
--    mappedRest = map (\y -> mmap' f y) xs

--mmap' f (List xs) = List(map (\y -> mmap' f y) xs)
mmap' f (List xs) = List(map (mmap' f) xs)


instance Mappable Tree where
    mmap f Empty = Empty
    mmap f (Node v l r) = Node (f v) (mmap f l) (mmap f r)

increaseAll :: (Enum a, Mappable m) => m a -> m a
increaseAll xs = mmap succ xs