Fixing semantics of makunbound.

* eval.c (unbound_s): New symbol variable.
(lookup_var): If a dynamic binding has the special sys:unbound
symbol as its value, then return nil, so the behavior
is as if there is no binding.
(makunbound): If the symbol exists in a dynamic environment,
then replace its value with sys:unbound, making it look
unbound.
(eval_init): Initialize unbound_s.

* lib.h (us_car, us_cdr): New inline functions.

* txr.1: New dialect notes under boundp.
Updated the makunbound documentation. Separated
makunbound documentation from fmakunbound and
mmakunbound. Added compatibility notes.

1 files changed, 2 insertions, 0 deletions

diff --git a/lib.h b/lib.h
index e8e6d4cd..c815658a 100644
--- a/lib.h
+++ b/lib.h
@@ -478,6 +478,8 @@ val type_check3(val obj, int, int, int);
 val class_check(val cobj, val class_sym);
 val car(val cons);
 val cdr(val cons);
+INLINE val us_car(val cons) { return cons->c.car; }
+INLINE val us_cdr(val cons) { return cons->c.cdr; }
 val rplaca(val cons, val new_car);
 val rplacd(val cons, val new_car);
 val sys_rplaca(val cons, val new_car);