aLib: RegExp - method to check if regexp describes empty language

alib/src/regexp/RegExp.cpp

@@ -70,6 +70,10 @@ void RegExp::setRegExp(RegExpElement* regExp) {
 	this->regExp = regExp;
 }
+bool RegExp::isEmpty() const {
+	return regExp == NULL || dynamic_cast<const RegExpEmpty*>(regExp);
+}
+
 void RegExp::toXML(ostream& out) {
 	RegExpPrinter::toXML(*this, out);
 }

alib/src/regexp/RegExp.h

@@ -55,6 +55,11 @@ public:
 	 */
 	void setRegExp(RegExpElement* regExp);
+	/**
+	 * @return true if regexp represents empty language
+	 */
+	bool isEmpty() const;
+
 	/**
 	 * Prints XML representation of the RegExp to the output stream.
 	 * @param out output stream to which print the RegExp