call-with-current-continuation

[Paul Haahr <haahr@mv.us.adobe.com>]

i retract what i said earlier about expecting to add call/cc to es.
the problem that es has with first class continuations is that, in
a shell, it must be possible to pass a first class value to an exec'ed
program.  i see no way to do that w/continuations.  that's one of
the reasons byron and i did not mention first class continuations
in our paper and why they do not appear on our todo list;  i regret
that i opened the door to them again, since we had months ago gone
down the path (in our heads) of trying to figure out what they meant
in the context of a shell, and concluded that they didn't make too
much sense.

that said, we're still open to being convinced that call/cc (or any
other experimental feature) does belong in the shell, but, remember,
some things that are entirely appropriate in some programming languages
may not fit in others, and complex features have implications that
pervade the design of whole systems.  call/cc, for example, affects
just about everything, at least from an implementation perspective.

paul