It would be misleading for consumers of the interface to mark compute_pi_digits awaitable -- at least in .NET world that have quite a lot of experience with asy

It would be misleading for consumers of the interface to mark compute_pi_digits awaitable -- at least in .NET world that have quite a lot of experience with async-await at this point. See http://blog.ploeh.dk/2016/04/11/async-as-surrogate-io/ http://blog.ploeh.dk/2016/04/11/async-as-surrogate-io/ for further discussion. Regular programmers are not using Task<T> as IO-monadic marker consciously, but they are surprised when a usage differs from that model.