Norman Ramsey and Simon Peyton Jones explain
cheap continuations
for C-- (a compiler back-end language), as opposed to (expensive)
first class continuations as in Scheme R5RS.
Coroutines and continuations are related concepts. Roberto
Ierusalimschy's
papers
include his 1994 "Revisiting Coroutines", with a very nice overview of
coroutine stuff. It seems to touch on every flavor of coroutine other
than Simon Peyton Jones's "cheap continuations". (He's also the
creator of Lua.)