diff --git a/lib/compiler.js b/lib/compiler.js
index 0800727..44c794d 100644
--- a/lib/compiler.js
+++ b/lib/compiler.js
@@ -182,43 +182,71 @@ PEG.Grammar.GrammarError.prototype = Error.prototype;
 /* ===== PEG.Grammar.* ===== */
 
 PEG.Grammar.Rule = function(name, displayName, expression) {
+  this.type = "rule";
   this.name = name;
   this.displayName = displayName;
   this.expression = expression;
 };
 
 PEG.Grammar.Choice = function(alternatives) {
+  this.type = "choice";
   this.alternatives = alternatives;
 };
 
-PEG.Grammar.Sequence = function(elements) { this.elements = elements; };
+PEG.Grammar.Sequence = function(elements) {
+  this.type = "sequence";
+  this.elements = elements;
+};
 
 PEG.Grammar.AndPredicate = function(expression) {
+  this.type = "and_predicate";
   this.expression = expression;
 };
 
 PEG.Grammar.NotPredicate = function(expression) {
+  this.type = "not_predicate";
   this.expression = expression;
 };
 
-PEG.Grammar.Optional = function(expression) { this.expression = expression; };
+PEG.Grammar.Optional = function(expression) {
+  this.type = "optional";
+  this.expression = expression;
+};
 
-PEG.Grammar.ZeroOrMore = function(expression) { this.expression = expression; };
+PEG.Grammar.ZeroOrMore = function(expression) {
+  this.type = "zero_or_more";
+  this.expression = expression;
+};
 
-PEG.Grammar.OneOrMore = function(expression) { this.expression = expression; };
+PEG.Grammar.OneOrMore = function(expression) {
+  this.type = "one_or_more";
+  this.expression = expression;
+};
 
 PEG.Grammar.Action = function(expression, action) {
+  this.type = "action";
   this.expression = expression;
   this.action   = action;
 };
 
-PEG.Grammar.RuleRef = function(name) { this.name = name; };
+PEG.Grammar.RuleRef = function(name) {
+  this.type = "rule_ref";
+  this.name = name;
+};
 
-PEG.Grammar.Literal = function(value) { this.value = value; };
+PEG.Grammar.Literal = function(value) {
+  this.type = "literal";
+  this.value = value;
+};
 
-PEG.Grammar.Any = function() {};
+PEG.Grammar.Any = function() {
+  this.type = "any";
+};
 
-PEG.Grammar.Class = function(characters) { this.characters = characters; };
+PEG.Grammar.Class = function(characters) {
+  this.type = "class";
+  this.characters = characters;
+};
 
 /* ===== Referenced Rule Existence Checks ===== */
 
@@ -967,7 +995,7 @@ PEG.Grammar.Action.prototype.compile = function(resultVar) {
 
   var expressionResultVar = PEG.Compiler.generateUniqueIdentifier("result");
 
-  if (this.expression instanceof PEG.Grammar.Sequence) {
+  if (this.expression.type === "sequence") {
     var params = PEG.ArrayUtils.map(
       PEG.ArrayUtils.range(1, this.expression.elements.length + 1),
       function(n) { return "$" + n; }