-- This is an algebraic data type:
data Pair = Pint Int Int | Pfloat Float Float
  deriving Show

-- | 
-- >>> x
-- Pint 6 7
x = Pint 6 7

-- | 
-- >>> y
-- Pfloat 6.0 7.0
y = Pfloat 6.0 7.0

-- | 
-- >>> firstOfPair x
-- 6
firstOfPair :: Pair -> Int
firstOfPair (Pint x y) = x

-- | 
-- >>> secondOfPair y
-- 7.0
secondOfPair :: Pair -> Float
secondOfPair p = case p of
    (Pfloat x y) -> y

-- This is how the actual True and False are implemented:
-- data Bool = True | False
data MyBool = MyTrue | MyFalse
  deriving Show

-- This is how the actual Maybe and nothing is implemented:
-- data Maybe a = Nothing | Just a
data MyMaybe a = MyNothing | MyJust a
  deriving Show

-- Destructure (unwrap Just), built in: fromJust
myFromJust :: MyMaybe a -> a
myFromJust (MyJust a) = a

-- | 
-- >>> myFromJust justThing
-- 5
justThing = MyJust 5

-- This is how the (:) list operator works:
data MyList a = Empty | MyCons a (MyList a)
  deriving (Show)

emptyList = Empty
oneBigList = MyCons 5 Empty
threeBigList = MyCons 3 (MyCons 4 (MyCons 5 Empty))

-- | 
-- >>> listSugar == listNoSugar
-- True
listEmpty = []
listSugar = [1,2,3]
listNoSugar = 1 : (2 : (3 : []))