Made regexps generated for empty character classes ("[]" and "[^]") work in IE.

lib/compiler.js

@@ -734,6 +734,18 @@ PEG.Grammar.Literal.prototype.compile = function(resultVar) {
 };
 
 PEG.Grammar.Class.prototype.compile = function(resultVar) {
+  /*
+   * Stupid IE considers regexps /[]/ and /[^]/ syntactically invalid, so we
+   * translate them into euqivalents it can handle.
+   */
+  if (this._characters === "") {
+    var regexp = "/^(?!)/";
+  } else if (this._characters === "^") {
+    var regexp = "/^[\\S\\s]/";
+  } else {
+    var regexp = "/^[" + this._characters + "]/";
+  }
+
   return PEG.Compiler.formatCode(
     "if (this._input.substr(this._pos).match(${regexp}) !== null) {",
     "  var ${resultVar} = this._input[this._pos];",
@@ -746,7 +758,7 @@ PEG.Grammar.Class.prototype.compile = function(resultVar) {
     "}",
     {
       characters: this._characters,
-      regexp:     "/^[" + this._characters + "]/",
+      regexp:     regexp,
       resultVar:  resultVar
     }
   );