void addFreeTypeListener(List<Type> types, FreeTypeListener ftl) {
        freeTypeListeners.put(ftl, freeVarsIn(types));
    }
void addFreeTypeListener ( List < Type > types , FreeTypeListener ftl ) { freeTypeListeners . put ( ftl , freeVarsIn ( types ) ) ; }
Add custom hook for performing post-inference action