OK,

I tried this one:

test:: IO (Maybe a)
test = return Nothing

It looks similar and it seems to work...

On Tue, Jan 5, 2021 at 8:22 PM Velichko Lefterov <velichko.lefterov@gmail.com> wrote:

Hello,

could someone explain me simple how return-type polymorphism works

in the following case:

newEmptyMVar :: IO (MVar a) ?

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