implementing a state machine using the "yield" keyword
Is it feasible to use the yield keyword to implement a simple state machine as shown here. To me it looks like the C# compiler has done the hard work for you as it internally implements a state machine to make the yield statement work.
Can you piggy-back on top of the work the compiler is already doing and get it to implement most of the state machine for you?
Has anyone done this, is it technically possible?
Answer
It's feasible but it is a bad idea. Iterator blocks were created to help you write custom iterators for collections, not for solving the general-purpose problem of implementing state machines.
If you want to write a state machine, just write a state machine. It's not hard. If you want to write a lot of state machines, write a library of useful helper methods that let you cleanly represent state machines, and then use your library. But don't abuse a language construct intended for something completely different that just happens to use state machines as an implementation detail. That makes your state machine code hard to read, understand, debug, maintain and extend.
(And incidentally, I did a double-take when reading your name. One of the designers of C# is also named Matt Warren!)