The structure continuation-data-type encapsulates continuations into a
data type as proposed by Marc Feeley on the Scheme Workshop 2001.
(continuation-capture receiver) -> continuation
Captures the current continuation of the expression and applies
RECEIVER to it. Unlike CALL-WITH-CURRENT-CONTINUATION applying the
continuation will immediately replace the current continuation.
(continuation-graft cont thunk) -> value of thunk
Makes the continuation CONT the current continuation and calls THUNK
afterwards.
(continuation-return cont . returned-values) -> returned-values
Makes the continuation CONT the current continuation and returns
RETURNED-VALUES afterwards.