Thanks for your comment.
I don't know how to feel about Protothreads. It's just syntatic sugar for using a state-machine to provide continuations. You're also not allowed to carry state over between continuations (although I can see how you can extend it to carry-over some struct of data or something). This greatly diminishes the usefulness of Protothreads.. so it feels more like a fun proof-of-concept.
Are there any popular/real-world use cases of Protothreads?