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User contributed comments, clarifications and examples
From Mark Feelys Paper pub/pdf-t1/feeley.pdf:
(continuation-capture receiver) – creates a continuation object representing the current continuation and tail-calls the receiver procedure with this continuation as the single argument.
(continuation-graft cont thunk) – calls the thunk with no argument and the implicit continuation cont.
(continuation-return cont value1...) – returns the value(s) to the continuation cont (the definition given above in terms of continuation-graft is still valid).