Am not sure about the relevance of this approach as i have very little experience with Haskell and FP. So it would be great if someone offers better solution. It's a valid approach. Rather than declare an Updateable class, I'd just have

On 2005 April 18 Monday 16:57, Dmitry Vyal wrote: the update function be a parameter of ins_in_tree. Also, the key and value types can be independent parameters of BinTree.

Why doesnt translator automatically deduce constraints in type of ins_in_tree and flat_tree functions so i need to explicitly define them? It deduces not just the constraints, but the entire type. You don't have to state the types of ins_in_tree or flat_tree at all. The following types are distinct (Ord a, Updateable a) => BinTree a -> a -> BinTree a BinTree a -> a -> BinTree a because the latter type has no constraints, and names having the latter type can be used in more contexts than the former. If foo :: BinTree a -> a -> BinTree a meant that foo might or might not have constraints, then there would be no way to tell the translator that foo has no constraints.

--------------- data (Ord a, Updateable a) => BinTree a = Leaf | Node (BinTree a) a (BinTree a)

class Updateable a where update :: a -> a

data Word_stat = Word_stat String Int deriving Show

instance Eq (Word_stat) where (==) (Word_stat s1 _) (Word_stat s2 _) = s1 == s2

instance Ord (Word_stat) where (Word_stat s1 _) < (Word_stat s2 _) = s1

instance Updateable (Word_stat) where update (Word_stat s i) = Word_stat s (i+1) -- inserts new element in the tree or updates existing one ins_in_tree :: (Ord a, Updateable a) => BinTree a -> a -> BinTree a ins_in_tree Leaf el = Node Leaf el Leaf ins_in_tree (Node left cur right) el

| el < cur = Node (ins_in_tree left el) cur right | el == cur = Node left (update cur) right | otherwise = Node left cur (ins_in_tree right el)

-- loads list of strings in the tree ins_list :: [String] -> BinTree Word_stat ins_list lst = foldl ins_in_tree Leaf (map wrap lst) where wrap :: String -> Word_stat wrap s = Word_stat s 1 --traverses the tree flat_tree :: (Ord a, Updateable a) => BinTree a -> [a] flat_tree Leaf = [] flat_tree (Node left el right) = (flat_tree left) ++ [el] ++ (flat_tree right)

-- function you probably need summary :: [String] -> [Word_stat] summary lst = flat_tree $ ins_list lst