No need for Sink.create arguments functions to return IO

[mariusmuja]

There is no need for Sink.create arguments functions to return IOs. Any side-effects that these functions might perform are suspended in the closures.

[fdietze]

I don't fully understand the reasoning behind the change. Could you please explain a bit more why we need Handler.create() to return IO but not Sink.create? How can this be still referentially transparent?

[mariusmuja]

This PR doesn't do anything with the return of Sink.create (doesn't try to fix #81), it only changes the type of the arguments of Sink.create (next, error and complete). I don't see a reason why these argument functions need to return IO types (even if they return IO types, the returned IOs are evaluated immediately).

[fdietze]

That makes sense, thanks for the explanation.