all tasks

Task/Singleton/Logtalk/singleton-1.logtalk

@@ -0,0 +1,16 @@
+:- object(singleton).
+
+    :- public(value/1).
+    value(Value) :-
+        state(Value).
+
+    :- public(set_value/1).
+    set_value(Value) :-
+        retract(state(_)),
+        assertz(state(Value)).
+
+    :- private(state/1).
+    :- dynamic(state/1).
+    state(0).
+
+:- end_object.

Task/Singleton/Logtalk/singleton-2.logtalk

@@ -0,0 +1,7 @@
+| ?- singleton::value(Value).
+Value = 0
+yes
+
+| ?- singleton::(set_value(1), value(Value)).
+Value = 1
+yes