loops - 在循环宏中使用照应绑定(bind)

Question

我有这样的结构

(loop :for c :in list-of-char-codes
      :if (gethash c hash-of-frequencies)
        :do (incf (gethash c hash-of-frequencies) 0))

是否有合理的方法来避免冗余 (gethash c hash-of-frequencies)，例如，使用照应宏？

Answer 1

您是否试图仅计算那些已经在hash-of-frequencies 中的字符？

(loop :for c :in list-of-char-codes
  :for freq = (gethash c hash-of-frequencies)
  :when freq
  :do (setf (gethash c hash-of-frequencies) (1+ freq)))

或者您可能想计算所有 个字符？

(loop :for c :in list-of-char-codes
  :do (incf (gethash c hash-of-frequencies 0)))