Added AndPredicate AST node.

This does not speed up the benchmark suite execution statistically significantly
on V8.

Detailed results (benchmark suite totals):

---------------------------------
 Test #     Before       After
---------------------------------
      1   28.72 kB/s   28.84 kB/s
      2   28.84 kB/s   28.76 kB/s
      3   28.83 kB/s   28.72 kB/s
      4   28.81 kB/s   28.84 kB/s
      5   28.76 kB/s   28.82 kB/s
---------------------------------
Average   28.79 kB/s   28.80 kB/s
---------------------------------

Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.9 Safari/533.2

lib/compiler.js

@@ -202,6 +202,10 @@ PEG.Grammar.ZeroOrMore = function(element) { this._element = element; };
 
 PEG.Grammar.OneOrMore = function(element) { this._element = element; };
 
+PEG.Grammar.AndPredicate = function(expression) {
+  this._expression = expression;
+};
+
 PEG.Grammar.NotPredicate = function(expression) {
   this._expression = expression;
 };
@@ -245,6 +249,9 @@ PEG.Grammar.extendNodes("checkReferencedRulesExist", {
   OneOrMore:
     function(grammar) { this._element.checkReferencedRulesExist(grammar); },
 
+  AndPredicate:
+    function(grammar) { this._expression.checkReferencedRulesExist(grammar); },
+
   NotPredicate:
     function(grammar) { this._expression.checkReferencedRulesExist(grammar); },
 
@@ -298,6 +305,11 @@ PEG.Grammar.extendNodes("checkNoLeftRecursion", {
       this._element.checkNoLeftRecursion(grammar, appliedRules);
     },
 
+  AndPredicate:
+    function(grammar, appliedRules) {
+      this._expression.checkNoLeftRecursion(grammar, appliedRules);
+    },
+
   NotPredicate:
     function(grammar, appliedRules) {
       this._expression.checkNoLeftRecursion(grammar, appliedRules);
@@ -917,6 +929,33 @@ PEG.Grammar.NotPredicate.prototype.compile = function(resultVar) {
   );
 };
 
+PEG.Grammar.AndPredicate.prototype.compile = function(resultVar) {
+  var savedPosVar                 = PEG.Compiler.generateUniqueIdentifier("savedPos");
+  var savedReportMatchFailuresVar = PEG.Compiler.generateUniqueIdentifier("savedReportMatchFailuresVar");
+  var expressionResultVar         = PEG.Compiler.generateUniqueIdentifier("result");
+
+  return PEG.Compiler.formatCode(
+    "var ${savedPosVar} = this._pos;",
+    "var ${savedReportMatchFailuresVar} = context.reportMatchFailures;",
+    "context.reportMatchFailures = false;",
+    "${expressionCode}",
+    "context.reportMatchFailures = ${savedReportMatchFailuresVar};",
+    "if (${expressionResultVar} !== null) {",
+    "  var ${resultVar} = '';",
+    "  this._pos = ${savedPosVar};",
+    "} else {",
+    "  var ${resultVar} = null;",
+    "}",
+    {
+      expressionCode:              this._expression.compile(expressionResultVar),
+      expressionResultVar:         expressionResultVar,
+      savedPosVar:                 savedPosVar,
+      savedReportMatchFailuresVar: savedReportMatchFailuresVar,
+      resultVar:                   resultVar
+    }
+  );
+};
+
 PEG.Grammar.RuleRef.prototype.compile = function(resultVar) {
   return PEG.Compiler.formatCode(
     "var ${resultVar} = this.${ruleMethod}(context);",

lib/metagrammar.js

@@ -357,9 +357,7 @@ PEG.grammarParser = (function(){
         this._pos = savedPos6;
       }
       var result36 = result37 !== null
-        ? (function() { 
+        ? (function() {  return new PEG.Grammar.AndPredicate((arguments[1]));  }).apply(this, result37)
-              return new PEG.Grammar.NotPredicate(new PEG.Grammar.NotPredicate((arguments[1])));
-             }).apply(this, result37)
         : null;
       if (result36 !== null) {
         var result30 = result36;

lib/metagrammar.pegjs

@@ -29,9 +29,7 @@ sequence
   / prefixed* { return $1.length != 1 ? new PEG.Grammar.Sequence($1) : $1[0]; }
 
 prefixed
-  : and suffixed {
+  : and suffixed { return new PEG.Grammar.AndPredicate($2); }
-      return new PEG.Grammar.NotPredicate(new PEG.Grammar.NotPredicate($2));
-    }
   / not suffixed { return new PEG.Grammar.NotPredicate($2); }
   / suffixed
 

test/compiler-test.js

@@ -193,8 +193,8 @@ test("buildParser reports missing referenced rules", function() {
     'start: "a" / "b" / missing',
     'start: missing*',
     'start: missing+',
-    'start: !missing',
     'start: &missing',
+    'start: !missing',
     'start: missing { }'
   ];
 
@@ -216,8 +216,8 @@ test("buildParser reports left recursion", function() {
     'start: "a" / "b" / start',
     'start: start*',
     'start: start+',
-    'start: !start',
     'start: &start',
+    'start: !start',
     'start: start { }',
 
     /* Indirect */

test/metagrammar-test.js

@@ -137,10 +137,7 @@ with (PEG.Grammar) {
 
   /* Canonical prefixed is "!\"abcd\"". */
   test("parses prefixed", function() {
-    grammarParserParses(
+    grammarParserParses('start: &"abcd"?', oneRuleGrammar(new AndPredicate(choice)));
-      'start: &"abcd"?',
-      oneRuleGrammar(new NotPredicate(new NotPredicate(choice)))
-    );
     grammarParserParses('start: !"abcd"?', oneRuleGrammar(new NotPredicate(choice)));
     grammarParserParses('start: "abcd"?',  oneRuleGrammar(choice));
   });