Implement no-loop rule attribute

lib/agenda.js

@@ -84,7 +84,7 @@ module.exports = declare(EventEmitter, {
 
         register: function (node) {
             var agendaGroup = node.rule.agendaGroup;
-            this.rules[node.name] = {tree: new AVLTree({compare: this.comparator}), factTable: new FactHash()};
+            this.rules[node.name] = { tree: new AVLTree({ compare: this.comparator }), factTable: new FactHash(), noLoop: {} };
             if (agendaGroup) {
                 this.addAgendaGroup(agendaGroup);
             }
@@ -162,6 +162,14 @@ module.exports = declare(EventEmitter, {
 
         insert: function (node, insert) {
             var rule = this.rules[node.name], nodeRule = node.rule, agendaGroup = nodeRule.agendaGroup;
+            if (nodeRule.noLoop) {
+                if (rule.noLoop[insert.hashCode]) {
+                    return;
+                }
+                else {
+                    rule.noLoop[insert.hashCode] = true;
+                }
+            }            
             rule.tree.insert(insert);
             this.getAgendaGroup(agendaGroup).insert(insert);
             if (agendaGroup) {

lib/parser/nools/tokens.js

@@ -94,6 +94,20 @@ var ruleTokens = {
         };
     })(),
 
+    noLoop: (function () {
+        var noLoopRegexp = /^(noLoop|no-loop)\s*:\s*(-?true|false)\s*[,;]?/;
+        return function (src, context) {
+            if (noLoopRegexp.test(src)) {
+                var parts = src.match(noLoopRegexp);
+                //
+                context.options.noLoop = Boolean(parts[2])
+                return src.replace(parts[0], "");
+            } else {
+                throw new Error("invalid format");
+            }
+        };
+    })(),
+
     "agenda-group": function () {
         return this.agendaGroup.apply(this, arguments);
     },
@@ -102,6 +116,10 @@ var ruleTokens = {
         return this.autoFocus.apply(this, arguments);
     },
 
+    "no-loop": function () {
+        return this.noLoop.apply(this, arguments);
+    },
+
     priority: function () {
         return this.salience.apply(this, arguments);
     },

lib/rule.js

@@ -208,6 +208,7 @@ var Rule = declare({
             this.name = name;
             this.pattern = pattern;
             this.cb = cb;
+            this.noLoop = options.noLoop;
             if (options.agendaGroup) {
                 this.agendaGroup = options.agendaGroup;
                 this.autoFocus = extd.isBoolean(options.autoFocus) ? options.autoFocus : false;

readme.md

@@ -37,6 +37,7 @@ Or [download the source](https://raw.github.com/C2FO/nools/master/nools.js) ([mi
       * [Structure](#rule-structure)
       * [Salience](#rule-salience)
       * [Scope](#rule-scope)
+	  * [no-loop](#rule-no-loop)
       * [Constraints](#constraints)
         * [Not](#not-constraint)
         * [Or](#or-constraint)
@@ -1001,6 +1002,33 @@ flow1
     });
 ```
 
+<a name="rule-no-loop"></a>
+### No-Loop
+
+When a rule's action modifies a fact it may cause the rule to activate again, causing an infinite loop. Setting no-loop to true will skip the creation of another Activation for the rule with the current set of facts.
+
+```javascript
+this.rule("Hello", {noLoop: true}, [Message, "m", "m.text like /hello/"], function (facts) {
+	var m = facts.m;
+	m.text = 'hello world';    
+	this.modify(m)
+});
+
+```
+Or using the DSL
+
+```javascript
+rule Hello {
+    no-loop: true;
+    when {
+        m: Message m.name like /hello/;
+    }
+    then { modify(m, function() {
+		m.text = 'hello world'
+	});
+}
+```
+
 
 
 <a name="rule-scope"></a>

test/flow/noLoop.test.js

@@ -0,0 +1,67 @@
+"use strict";
+var it = require("it"),
+    assert = require("assert"),
+    nools = require("../../");
+
+it.describe("no-loop", function (it) {
+    /*jshint indent*/
+    function Message(name) {
+        this.name = name;
+    }
+    var cnt = 0;   
+
+    var flow1 = nools.flow("noLoop1", function () {
+
+        this.rule("Hello2", { noLoop: true }, [Message, "m", "m.name =~ /Hello/"], function (facts) {
+            var m = facts.m;
+            m.name = 'Hello World';
+            this.modify(m);
+        });
+    }),
+
+        flow2 = nools.flow("noLoop2", function () {
+
+            this.rule("Hello1", [Message, "m", "m.name =~ /Hello/"], function (facts) {
+                var m = facts.m;
+                if (cnt++ < 2) {
+                    m.name = 'Hello World';
+                    this.modify(m);
+                }
+            });
+        });
+
+    var noolsSource =  "rule 'Hello3' { no-loop: true; when {m: Message m.name =~/Hello/;}then {modify(m, function () { this.name = 'Hello World'; });}}";
+
+    var flow3 = nools.compile(noolsSource, {
+        name: 'testDsl'
+        ,define: {
+            Message: Message
+        }
+    });
+
+    it.should("not loop with option on and loop otherwise", function () {
+        var fired1 = [], fired2 = [], fired3 = [];
+        var session1 = flow1.getSession(new Message("Hello")).on("fire", function (name) {
+            fired1.push(name);
+        }),
+        session2 = flow2.getSession(new Message("Hello")).on("fire", function (name) {
+            fired2.push(name);
+        }),
+        session3 = flow3.getSession(new Message("Hello")).on("fire", function (name) {
+            fired3.push(name);
+        });
+        return session1.match()
+            .then(function () {
+        return session2.match().then(function () {
+            return session3.match().then(function () {
+            })
+        })
+        })
+       .then(function () {
+            assert.deepEqual(fired1, ["Hello2"]);
+            assert.deepEqual(fired2, ["Hello1", "Hello1", "Hello1"]);
+            assert.deepEqual(fired3, ["Hello3"]);
+        });
+    });
+
+});