type Point = Point x y

instance Show Point where
  show (Point x y) = "Point " ++ (show x) ++ " " ++ (show y)

instance Name Point where
  getField nm (Point x y)
    | nm == "x" = x
    | nm == "y" = y
    | else = fail "Undefined name."
  isField nm _ = nm == "x" || nm == "y"

pointX = flip Point 0

pointY = Point 0

pointEmpty = Point 0 0

type Circle = Circle x y z

instance Show Circle where
  show (Circle x y z) =
    "Circle " ++ (show x) ++ " " ++ (show y) ++ " " ++ (show z)

instance Name Circle where
  getField nm (Circle x y z)
    | nm == "x" = x
    | nm == "y" = y
    | nm == "z" = z
    | else = fail "Undefined name."
  isField nm _ = nm == "x" || nm == "y" || nm == "z"

circleXZ = flip Circle 0

circleX x = Circle x 0 0

circleYZ = Circle 0

circleY y = Circle 0 y 0

circleZ = Circle 0 0

circleEmpty = Circle 0 0 0