Jan Burse, erstellt 17. Aug 2019
* The system predicate sys_unbind/1 installs an unbind handler and
* immediately succeeds. The unbind handler is invoked during a redo or
* a close. In contrast to a cutter the unbind handler is not invoked
* when choice points are removed. When the unbind handlers are executed
* exceptions are aggregate_alld that are possibly thrown by the unbind
* handlers. When unbind handler fails a directive failed error is thrown.
* The predicate sys_freeze_var/2 will create a new reference object that
* captures the given variable. The reference object will have a stable
* hash, equal and lexical ordering for the duration of the continuation.
* The predicate sys_melt_var/2 allows retrieving the term the variable
* is currently instantiated to. The predicate sys_bound_var/1 allows
* checking whether the variable is currently instantiated or not.
* Warranty & Liability
* To the extent permitted by applicable law and unless explicitly
* otherwise agreed upon, XLOG Technologies GmbH makes no warranties
* regarding the provided information. XLOG Technologies GmbH assumes
* no liability that any problems might be solved with the information
* provided by XLOG Technologies GmbH.
* Rights & License
* All industrial property rights regarding the information - copyright
* and patent rights in particular - are the sole property of XLOG
* Technologies GmbH. If the company was not the originator of some
* excerpts, XLOG Technologies GmbH has at least obtained the right to
* reproduce, change and translate the information.
* Reproduction is restricted to the whole unaltered document. Reproduction
* of the information is only allowed for non-commercial uses. Selling,
* giving away or letting of the execution of the library is prohibited.
* The library can be distributed as part of your applications and libraries
* for execution provided this comment remains unchanged.
* Only to be distributed with programs that add significant and primary
* functionality to the library. Not to be distributed with additional
* software intended to replace any components of the library.
* Jekejeke is a registered trademark of XLOG Technologies GmbH.
* The predicate installs an unbind handler A and immediately succeeds.
* The unbind handler is invoked during a redo or a close.
* sys_freeze_var(V, R):
* The predicate succeeds when R unifies with a new references
* object that captures the variable V.
% sys_freeze_var(+Var, -Ref)
sys_freeze_var/2, 'SpecialUndo', 1).
* sys_melt_var(R, T):
* The predicate succeeds when T unifies with the variable captured
* by the reference object R.
% sys_melt_var(+Ref, -Var)
sys_melt_var/2, 'SpecialUndo', 2).
* The predicate succeeds when the variable captured by the reference
* object R is currently instantiated.
sys_bound_var/1, 'SpecialUndo', 3).
* The predicate succeeds when R is a reference to a variable.