Modul State

 Jan Burse, erstellt 17. Aug 2019 
/**


 * This module provides trailed named values.


 *


 * 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.


 *


 * Restrictions


 * 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.


 *


 * Trademarks


 * Jekejeke is a registered trademark of XLOG Technologies GmbH.


 */




:- package(library(jekmin/reference/term)).




:- module(state, []).




:- use_module(library(experiment/trail)).


:- use_module(library(minimal/assume)).


:- use_module(library(experiment/ref)).




:- private state/2.


:- thread_local state/2.




/**************************************************************/


/* Trailed Shared                                             */


/**************************************************************/




/**


 * b_setval(K, W):


 * The predicate assigns the value W to the key K.


 * The assignment is automatically undone upon backtracking.


 */


% b_setval(+Term, +Term)


:- public b_setval/2.


b_setval(K, W) :-


   b_delete(K),


   sys_freeze_var(H, F),


   H = wrap(W),


   assumable_ref(state(K, F), R),


   depositz_ref(R).




/**


 * nb_current(K, W):


 * The predicate succeeds for the value W of the key K.


 */


% nb_current(-Term, -Term)


:- public nb_current/2.


nb_current(K, W) :-


   state(K, F),


   sys_melt_var(F, wrap(W)).




/**


 * b_delete(K):


 * The predicate de-assigns the key K.


 * The de-assignment is automatically undone upon backtracking.


 */


% b_delete(+Term)


:- public b_delete/1.


b_delete(K) :- ground(K), !,


   b_delete2(K).


b_delete(_) :-


   throw(error(instantiation_error, _)).




% b_delete2(+Term)


:- private b_delete2/1.


b_delete2(K) :-


   clause_ref(state(K, _), true, R), !,


   withdrawz_ref(R).


b_delete2(_).

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