newtype_test.hs

module Main where

newtype HasName a =
  HasName (a -> String)

data A = A deriving (Show)
data B = B deriving (Show)
data C = C deriving (Show)

aName :: HasName A
aName = HasName $ const "A"

bName :: HasName B
bName = HasName $ const "B"

cName :: HasName C
cName = HasName $ const "C"

dispatch :: Int -> HasName A -> HasName B -> HasName (Either A B)
dispatch 0 (HasName a) _ = HasName (\(Left A) -> a A)
dispatch 1 _ (HasName b) = HasName (\(Right B) -> b B)