lesson1.elm

data Color = Red | Black | Rgb Int Int Int

toString : Color -> String
toSring color =
  case color of
    Red -> "Red"
    Black -> "Black"
    Rgb r g b -> "Other"


data List = Empty | NotEmpty Int List

--list = NotEmpty 1 (NotEmpty 2 (NotEmpty 3 Empty))
list = 1 :: 2 :: 3 :: [] -- 1,2,3

--length list =
--  case list of
--    Empty -> 0
--    NotEmpty n rest -> 1 + length rest

length list =
  case list of
    [] -> 0
    n :: rest -> 1 + length rest

sum : List -> Int
sum list = 
  case list of
    Empty -> 0
    NotEmpty n rest -> n + sum rest
    
--squareAll list =
--  case list of
--    Empty -> Empty
--    NotEmpty n rest -> NotEmpty (n^2) (squareAll rest)

squareAll list = map (\x -> x^2) list

incrementAll list = map (\x -> x + 1) list

map : (a -> b) -> [a] -> [b]

map f list =
  case list of
    [] -> []
    n :: rest -> f n :: map f rest


--add a b = a + b
add = \a -> \b -> a + b

reduce : (a -> b -> b) -> b -> [a] -> b
reduce accumulate base list =
  case list of
    [] -> base
    n :: reset -> accumulate n (reduce accumulate base rest)

--length list = reduce (\n acc -> acc + 1) 0 list

data Boolean = Tru
  | Fls
  | Not Boolean
  | And Boolean Boolean
  | Or Boolean Boolean
  
expr = Or (Not Tru) Fls
eval : Boolean -> Bool
eval boolean =
  case boolean of
    Fls -> False
    Tru -> True
    Not b -> not (eval b)
    And b1 b2 -> eval b1 && eval b2
    Or b1 b2 -> eval b1 || eval b2

data Tree a = Node a (Tree a) (Tree a) | EmptyTree

sum : Tree Int -> Int
sum tree =
  case tree of
    EmptyTree -> 0
    Node x left right -> n + sum left + sum right

main = asText (eval expr)