Allow RegEx matches of length 0. This seems more correct to me. (However, this is not super important in practice. Grammar files should not contain regular expressions that could match the empty string; if such a RegEx matched 0 characters once, it would match again and again forever, since it wouldn't consume any input.)

src/RegEx.cpp

@@ -233,12 +233,13 @@ RegEx::~RegEx() {
 }
 
 int RegEx::longMatch(std::string stringToMatch) {
-	//If the beginning character is wrong, exit immediantly. Otherwise, get all the states we can get from adding the second character to the state where we accepted the first
+	// Start in the begin state (only).
 	int lastMatch = -1;
-	currentStates = *(begin->advance(stringToMatch[0]));
+	currentStates.clear();
+	currentStates.push_back(begin);
 	std::vector<RegExState*> nextStates;
 
-	for (int i = 1; i < stringToMatch.size(); i++) {
+	for (int i = 0; i < stringToMatch.size(); i++) {
 		//Go through every current state. Check to see if it is goal, if so update last goal.
 		//Also, add each state's advance to nextStates
 		for (std::vector<RegExState*>::size_type j = 0; j < currentStates.size(); j++) {
@@ -292,6 +293,7 @@ void RegEx::test() {
     {
         RegEx re("a*");
         assert(re.longMatch("aa") == 2);
+        assert(re.longMatch("b") == 0);
     }
 
     std::cout << "RegEx tests pass\n";