{-# LANGUAGE MultiParamTypeClasses #-}
data E1 = E1
data E2 = E2
data P1 = P1
data P2 = P2
class Has en pr
instance Has E1 P1
instance Has E1 P2
instance Has E2 P2

-- do something useful
foo :: Has en pr => en -> pr -> IO ()
foo _ _ = return ()

main :: IO ()
main = foo E2 P1