It means that the function can return an mvar containing any type that you need. What type it returns depends on what type your program asks for.
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 <
[hidden email]> wrote:
Hello,
could someone explain me simple how return-type polymorphism works
in the following case:
newEmptyMVar :: IO (MVar a) ?
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