detector song; 
 to get the filename
  detector lyrics; 
 extracts lyrics
  detector melody; 
 extracts melody
  detector check;  
 to walk the tree
  
  atom str name;
  atom str text;
  atom str note;  
  
  midi: song;
  
  song: file lyrics melody check;
  
  file: name;
  
  lyrics: text*;
  melody: note*;