docs: def p_array(self,t):
      """expression : '{' commalist '}'
                    | kw_array '[' commalist ']'
      """
      if len(t)==4: t[0] = ArrayLit(t[2].children)
      elif len(t)==5: t[0] = ArrayLit(t[3].children)
      else: raise NotImplementedError('unk_len',len(t)) # pragma: no cover