Comparison: How simplified subsumption interacts with newtype and with type aliases

simplified_subsumption.hs

{-# LANGUAGE RankNTypes #-}
import Control.Monad.Cont (MonadIO)

-- Comparison: How simplified subsumption interacts with newtype and with type aliases

-- example with type alias:

type Foo a = forall m. MonadIO m => m a

foo :: forall m a. MonadIO m => Int -> m a
foo = foo

bar :: MonadIO m => (Int -> Foo ()) -> m ()
-- doesn't work with 9.2.2
-- bar = ($ 1)
bar x = x 1

baz :: MonadIO m => m ()
-- doesn't work with 9.2.2, works with 8.10.7
-- baz = bar foo
-- works with ghc 8.10.7 and 9.2.2
baz = bar (\x -> foo x)

-- equivalent example with newtype:

newtype FooN a = FooN { unFooN :: forall m. MonadIO m => m a}

unFooN2 :: MonadIO m => FooN a -> m a
unFooN2 (FooN m) = m

barN :: MonadIO m => (Int -> FooN ()) -> m ()
-- the generated field selector unFooN only works with 8.10.7
barN = unFooN2 . ($ 1)

bazN :: MonadIO m => m ()
-- !!! doesn't even work with ghc 8.10.7 !!!
-- bazN = barN (FooN . foo)
-- works with ghc 8.10.7 and 9.2.2
bazN = barN (\x -> FooN (foo x))