Scheme Request for Implementation 226,
by Marc Nieper-Wißkirchen,
is now available for discussion.
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Here's the abstract:
This SRFI defines a rich set of control operators for the Scheme
programming language, including the venerable call/cc
(call-with-current-continuation). The set of operators was highly
influenced by the control operators provided by Racket.
Continuations can be delimited by continuation prompts, and all
continuations become delimited continuations, at the latest by the
default prompt at the start of each thread. Moreover, continuations
are divided into composable and non-composable continuations, which
can be captured and reinstated.
To investigate continuations, this SRFI supports continuation marks
and offers operators to set and retrieve them. Moreover, this SRFI
defines clear semantics of exceptions, parameter objects, promises,
and threads consistent with the other concepts defined here.