The easiest way to add code to Marsyas is to add a test to apps/mudbox/mudbox.cpp. This file is a huge mess of short examples, many out of date and no longer working, but it seems popular.
To add your own test, follow the general pattern of other tests. You will need to modify
void printHelp(string progName): display the argument which calls your test.
int main(int argc, const char **argv): call your test function. Yes, that's a 100-line collection of
else ifstatements. (see “huge mess”, above)
void test_myTestName(): your actual code.