{-# language UndecidableSuperClasses #-}

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

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

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

test1
  :: forall c m. c ~ (MonadReader () & MonadReader Double & MonadIO)
  => c m => m Int
test1 = example @c (pure 1)

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

main = pure ()