From 24b78dbf8bd2a6644e50e88c010eb650e7784d94 Mon Sep 17 00:00:00 2001
From: vsc <vsc@b08c6af1-5177-4d33-ba66-4b1c6b8b522a>
Date: Sun, 16 Jul 2006 01:41:07 +0000
Subject: [PATCH] an implementation of queues in the DB.

git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1674 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
---
 library/dbqueues.yap | 46 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 library/dbqueues.yap

diff --git a/library/dbqueues.yap b/library/dbqueues.yap
new file mode 100644
index 000000000..2cbf74eb1
--- /dev/null
+++ b/library/dbqueues.yap
@@ -0,0 +1,46 @@
+:- module(dbqueue, [
+	db_enqueue/2,
+	db_dequeue/2,
+	db_clean_queue/1	  
+		 ]).
+
+
+:- unhide('$init_db_queue').
+:- unhide('$db_enqueue').
+:- unhide('$db_dequeue').
+
+
+db_enqueue(Name,El) :- var(Name),
+	throw(error(instantiation_error(Name),db_enqueue(Name,El))).
+db_enqueue(Name,El) :- \+ atom(Name), !,
+	throw(error(type_error_atom(Name),db_enqueue(Name,El))).
+db_enqueue(Name,El) :-
+	recorded('$db_queue',[Name|Ref],_), !,
+	prolog:'$db_enqueue'(Ref, El).
+db_enqueue(Name,El) :-
+	prolog:'$init_db_queue'(Ref),
+	recorda('$db_queue',[Name|Ref],_),
+	prolog:'$db_enqueue'(Ref,El).
+
+
+db_dequeue(Name,El) :- var(Name),
+	throw(error(instantiation_error(Name),db_dequeue(Name,El))).
+db_dequeue(Name,El) :- \+ atom(Name), !,
+	throw(error(type_error_atom(Name),db_dequeue(Name,El))).
+db_dequeue(Name,El) :-
+	recorded('$db_queue',[Name|Ref],R),
+	( prolog:'$db_dequeue'(Ref, El) ->
+	    true
+	;
+	    erase(R),
+	    fail
+	).
+
+db_clean_queue(Name) :-
+	recorded('$db_queue',[Name|Ref],R), !,
+	erase(R),
+	db_dequeue_all(Ref).
+db_clean_queue(_).
+
+db_dequeue_all(Ref) :-
+	( prolog:'$db_dequeue'(Ref, _) -> db_dequeue_all(Ref) ; true ).