- SCM proc = ly_lily_module_constant ("percussion?");
- SCM drums = scm_call_1 (proc, ly_symbol2scm (instrument_string_.c_str ()));
- audio_staff->percussion_ = (drums == SCM_BOOL_T);
+ SCM drums = Lily::percussion_p (ly_symbol2scm (instrument_string_.c_str ()));
+ audio_staff->percussion_ = to_boolean (drums);