type Name = [Char]
type Score = Int
data Kind = Assignment | Exam | Quiz
    deriving (Eq, Ord, Show)

-- A "named tuple" for representing entries in a "gradebook"

data GradeEntry = Entry Name Kind Score
    deriving (Show)

-- Implementing a different Ord functionality -- we only look
-- at scores when comparing

instance Ord GradeEntry where
  compare (Entry _ _ score1) (Entry _ _ score2) 
   | score1 > score2 = GT
   | score1 < score2 = LT
   | otherwise = EQ

-- A goofy version of == for GradeEntries that only looks at
-- the names.  We define our own "==" function.

instance Eq GradeEntry where
  (Entry name1 _ _) == (Entry name2 _ _)  =  name1 == name2


getScore (Entry _ _ points) = points

entries = [Entry "Brad" Assignment 87, Entry "Brad" Exam 35, Entry "Bob" Quiz 100]


data Coord = Cartesian Float Float | Polar Float Float

{-
distance (Cartesian x y) = ...

distance (Polar r theta) = ...
-}

-- Our first recursive type -- Nat is on left and right

data Nat = Zero | Succ Nat
  deriving (Eq, Ord, Show)

natToInt Zero = 0
natToInt (Succ n) = 1 + natToInt n

-- Another recursive type.  Could implement our own lists!

data IntList = Empty | LNode Int IntList
  deriving (Eq, Ord, Show)

sumIL Empty = 0
sumIL (LNode num rest) = num + (sumIL rest)

-- Polymorphic type definition.  Give me a type for a, and
-- an AnyList is an a followed by an AnyList of a's.

data AnyList a = Nil | ALNode a (AnyList a)
  deriving (Eq, Show)


data Possibly a = Fail | Ok a
  deriving (Eq, Ord, Show)


firstSatisfying p [] = Fail
firstSatisfying p (x:xs) 
 | p x = Ok x
 | otherwise = firstSatisfying p xs