code: def p_genvarlist(self, p):
          'genvarlist : genvarlist COMMA genvar'
          p[0] = p[1] + (p[3],)
          p.set_lineno(0, p.lineno(1)f p_genvarlist(self, p):
          'genvarlist : genvarlist COMMA genvar'
          p[0] = p[1] + (p[3],)
          p.set_lineno(0, p.lineno(1))
docs: genvarlist : genvarlist COMMA genvar