Implementing sys:abscond-from operator.

* eval.c (sys_abscond_from_s): New symbol variable.
(op_abscond_from): New static function.
(do_expand): Handle abscond-from like return-from.
(eval_init): Initialize sys_abscond_from_s and
register sys:abscond-from operator.

* share/txr/stdlib/yield.tl  (yield-from): Use
sys:abscond-from instead of return-from, to avoid
tearing down the continuation's resources that it may
need when restarted.

* txr.1: Documented sys:abscond-from and added
a mention to the Delimited Continuations introduction.

* unwind.c (uw_abscond_to_exit_point): New static function.
(uw_block_abscond): New function.

* unwind.h (uw_block_abscond): Declared.

1 files changed, 1 insertions, 0 deletions

diff --git a/unwind.h b/unwind.h
index a9b456ae..bcf8d185 100644
--- a/unwind.h
+++ b/unwind.h
@@ -102,6 +102,7 @@ INLINE val uw_block_return(val tag, val result)
 {
    return uw_block_return_proto(tag, result, nil);
 }
+val uw_block_abscond(val tag, val result);
 void uw_push_catch(uw_frame_t *, val matches);
 void uw_push_handler(uw_frame_t *, val matches, val fun);
 noreturn val uw_throw(val sym, val exception);