{-# language UndecidableSuperClasses #-}

import Control.Monad.Reader.Class (MonadReader)
import Control.Monad.IO.Class (MonadIO)

class (c1 m, c2 m) => Combine c1 c2 m
instance (c1 m, c2 m) => Combine c1 c2 m

example :: c m => (forall m. c m => m a) -> m a
example a = a

test1 :: (MonadReader () m, MonadReader Double m, MonadIO m) => m Int
test1 = example @(Combine (MonadReader ()) (Combine (MonadReader Double) MonadIO)) (pure 1)

test2 :: MonadReader Char m => m Bool
test2 = example @(MonadReader Char) (pure False)

main = pure ()