code: def t_FIELD(t):
      r'[A-Za-z_][\w_]*'
      if t.value in u_ops:
          t.type = 'U_OP'
      elif t.value in b_ops:
          t.type = 'B_OP'
      return f t_FIELD(t):
      r'[A-Za-z_][\w_]*'
      if t.value in u_ops:
          t.type = 'U_OP'
      elif t.value in b_ops:
          t.type = 'B_OP'
      return t
docs: r'[A-Za-z_][\w_]*