elm-binary-tree.elm

sum : Tree Int -> Int
sum tree = 
    case tree of
      Empty -> 0
      Node v left right ->
         v + sum left + sum right

flatten : Tree a -> List a
flatten tree =
    case tree of
      Empty -> []
      
      Node v left right -> flatten left ++ [v] ++ flatten right

isElement : a -> Tree a -> Bool
isElement e tree =
    case tree of 
      Empty -> False
      
      Node v left right -> 
          if e == v then
              True
          else
              (isElement e left) || (isElement e right)
       
fold : (a -> b -> b) -> b -> Tree a -> b
fold f a tree =
    case tree of
      Empty -> a
      
      Node v left right -> 
          fold f (fold f (f v a) left) right

sum' : Tree Int -> Int
sum' tree = fold (+) 0 tree

flatten' : Tree a -> List a
flatten' tree = fold (::) [] tree
  
isElement' : a -> Tree a -> Bool
isElement' t tree = 
    fold (\x y -> (x==t) || y) False tree

preorder : Tree a -> List a
preorder tree =
    case tree of
      Empty -> []

      Node v left right -> 
          [v] ++ preorder left ++ preorder right

inorder : Tree a -> List a
inorder tree =
    case tree of
      Empty -> []

      Node v left right -> 
          preorder left ++ [v] ++ preorder right

postorder : Tree a -> List a
postorder tree =
    case tree of
      Empty -> []

      Node v left right -> 
          preorder left ++ preorder right ++ [v]