JobDescription.hs

class HasN a where
  n :: a -> Int

data JobOne = JobOne Int
data JobTwo = JobTwo
data JobThree = JobThree Int

data JobDescriptionWithN = JobDescriptionWithNOne JobOne | JobDescriptionWithNThree JobThree
data JobDescription = JobDescriptionTwo JobTwo | JobWithN JobDescriptionWithN

instance HasN JobOne where
  n (JobOne x) = x

instance HasN JobThree where
  n (JobThree x) = x

instance HasN JobDescriptionWithN where
  n (JobDescriptionWithNOne j) = n j
  n (JobDescriptionWithNThree j) = n j

main = print . n $ JobOne 1