data Tree a = Nil | Branch (Tree a) a (Tree a)

tInsert value Nil = Branch Nil value Nil
tInsert value (Branch lt v rt) = if value > v then Branch lt v (tInsert value rt)
                                            else Branch (tInsert value lt) v rt

tFind value Nil = False
tFind value (Branch lt v rt) =
    if value == v then True
    else if value < v then tFind value lt
       else tFind value rt

treeToList Nil = []
treeToList (Branch lt v rt) = treeToList lt++[v]++treeToList rt

data I7 = I7 Int 

instance Num I7 where
        I7 a + I7 b = I7 $(a + b) `mod` 7
        I7 a - I7 b = I7 $(a - b) `mod` 7
        I7 a * I7 b = I7 $(a * b) `mod` 7
        abs = id
        signum (I7 0) = 0
        signum _ = 1
        fromInteger a = I7 $ fromInteger a `mod` 7
instance Eq I7 where
        I7 a == I7 b =  a == b
instance Ord I7 where
        compare (I7 a) (I7 b) = compare a b

instance Show I7 where
    show (I7 a) = show a ++ "_7"

instance Show a => Show (Tree a) where
    show Nil = "."
    show (Branch lt v rt) =
      "[" ++ show lt ++ " " ++ show v ++ " " ++ show rt ++ "]"

instance Eq a => Eq (Tree a) where
    (Branch lt1 v1 rt1) == (Branch lt2 v2 rt2) =
     (lt1 == lt2) && (v1 == v2) && (rt1 == rt2)
    Nil == Nil = True
    _ == _ = False

instance Functor Tree where
  fmap f Nil = Nil
  fmap f (Branch lt v rt) = Branch (fmap f lt) (f v) (fmap f rt)

instance Foldable Tree where
  foldr f a Nil = a
  foldr f a (Branch lt v rt) = 
    let b = foldr f a rt
        c = f v b 
    in foldr f c lt

import Data.Foldable
treeToList' = toList