update README: backtrackable globals
@@ -47,6 +47,7 @@ Extend Scryer Prolog to include the following, among other features:
* All-solutions predicates (`findall/{3,4}`, `bagof/3`, `setof/3`) (_done_).
* Clause creation and destruction (`asserta/1`, `assertz/1`,
`retract/1`, `abolish/1`) with logical update semantics (_done_).
+* Backtrackable global variables via `bb_get/2` and `bb_put/2` (_done_).
* Streams and predicates for stream control (_in progress_).
* An incremental compacting garbage collector satisfying the five
properties of "Precise Garbage Collection in Prolog."
@@ -140,6 +141,8 @@ The following predicates are built-in to Scryer.
* `atom/1`
* `atomic/1`
* `bagof/3`
+* `bb_get/2`
+* `bb_put/2`
* `between/3`
* `call/1..62`
* `call_cleanup/2`
