main.hs

-- Also note, it seems people generally reach for positional types unless the data has many fields.
-- data BTNode t = BTNode t (BTNode t) (BTNode t) | BTNil
-- as opposed to:
-- data BTNode t = BTNode { data :: t, left :: BTNode, right :: BTnode } | BTNil

data Car2 = Car2 { make :: Maybe String } deriving (Show)

-- Haskell automatically makes a function in this scope:
-- make :: Car2 -> Maybe String
-- So you can just say `make c1` to get the make of the Car2 called `c1`.

carMake :: Car2 -> Maybe String
carMake (Car2 x) = x

c1 = Car2 Nothing
definitelyTrue = carMake c1 == make c1