{-# LANGUAGE LambdaCase #-}

data Planet = Earth | Mercury | Venus | Mars | Jupiter | Saturn | Uranus | Neptune
  deriving (Eq)

ageOn :: Planet -> Float -> Float
ageOn = flip (/) . (earthSecondsPerYear *) . earthSecondsFor
  where
    earthSecondsPerYear = 31557600
    earthSeconds =
      \case Earth -> 1
            Mercury -> 0.2408467
            Venus -> 0.61519726
            Mars -> 1.8808158
            Jupiter -> 11.862615
            Saturn -> 29.447498
            Uranus -> 84.016846
            Neptune -> 164.79132