As some of you may be aware, CVS HEAD boast preliminary, and
as-of-yet-unsupported alien callback functionality.
The interface issues are currently on the table at sbcl-devel.
If you are a potential user of this functionality, please familiarize
yourself with the discussion so far, and comment if you feel that
your needs and viewpoints are not yet represented.
The current issues are in the thread starting from "Callbacks, details,
-- Nikodemus Schemer: "Buddha is small, clean, and serious."
Lispnik: "Buddha is big, has hairy armpits, and laughs."