[Sam]
... Except that since the escape procedure is 'first-class' it can be stored away and invoked (and reinvoked) later. [that's all that 'first-class' means: a thing that can be stored in a variable, returned from a function, used as an argument, etc..]
I've never seen a let/cc that wasn't full-blown, but it wouldn't surprise me.
The let/cc's in question were specifically defined to create continuations valid only during let/cc's dynamic extent, so that, sure, you could store them away, but trying to invoke one later could be an error. It's in that sense I meant they weren't "first class". Other flavors of Scheme appear to call this concept "weak continuation", and use a different verb to invoke it (like call-with-escaping-continuation, or call/ec). Suspect the let/cc oddballs I found were simply confused implementations (there are a lot of amateur Scheme implementations out there!).
Would full-blown coroutines be powerful enough for your needs?
Yes, I think they would be. But I think with Python it's going to be just about as hard, either way.
Most people on this list are comfortable with coroutines already because they already understand them -- Jeremy can even reach across the hall and hand Guido a helpful book <wink>. So pondering coroutines increase the number of brain cells willing to think about the implementation. continuation-examples-leave-people-still-going-"huh?"-after-an- hour-of-explanation-ly y'rs - tim