Case between two unrelated types in Haskell

Question

Is it possible to use case expression between two unrelated types in Haskell, like in this example (not working) code:

data A = A
data B = B

f x = case x of
  A -> 1
  B -> 2

main = do
  print $ test A
  return ()

I know I can use Either here, but this code is not meant to be used - I want to deeply learn the Haskell type system and see what could be done.

Answer 1

A and B are distinct types. If you want a function that can take values of multiple types, you need a typeclass.

data A = A
data B = B

class F a where
  f :: a -> Int

instance F A where
  f _ = 1

instance F B where
  f _ = 2

main = do
  print $ f A