Frontend and backend communication

[Dainius (GreatEmerald)]

No no. It's the other way round. Shuffle() is in the library
(backend). PlaySound() is in the executable (frontend). Since I don't
want the library to be dependent on any sound libraries, I can't have
PlaySound() in it. And there is no other way that I can think of to
execute PlaySound() just at the end of Shuffle() without capturing
events (since Shuffle() itself is called by a whole lot of different
functions across the library, and not from the executable itself).