small fixes

ml.cpp

@@ -477,7 +477,7 @@ MlValue MlValue::operator%(const MlValue &other) const {
 }
 
 // Get the name of the type of this value
-std::string MlValue::get_type_name() {
+std::string MlValue::get_type_name() const {
 	switch (type) {
 		case QUOTE:
 			return QUOTE_TYPE;
@@ -1524,7 +1524,6 @@ namespace builtin {
 	MlValue sprintf(std::vector<MlValue> args, MlEnvironment &env) {
 		eval_args(args, env);
 
-		std::string result;
 		if (args.size() < 1 || args.size() > 2)
 			throw MlError(MlValue("sprintf", sprintf), env, args.size() > 2 ? TOO_MANY_ARGS : TOO_FEW_ARGS);