如何在任意点退出函数,在elisp中

Question

这是一个简单的问题,但不知何故,我无法通过谷歌搜索找到答案:

如果不满足某些条件,如何在任意执行点退出函数.例如(我在这里使用"(exit)"代替):

(defun foo ()
  (progn (if (/= a1 a2)
             (exit) ; if a1!=a2, exit the function somehow
           t)
         (blahblah...)))

Answer 1

在elisp中,您可以使用catch而throw 不是cl block和return-from.

(defun foo ()
  (catch 'my-tag
    (when (not (/= a1 a2))
      (throw 'my-tag "non-local exit value"))
    "normal exit value"))

看到 C-hig (elisp) Nonlocal Exits RET

Answer 2

在身体周围放一块并从中返回:

(require 'cl-macs)
(defun foo ()
  (block foo
    (if (/= a1 a2)
        (return-from foo)
        reture-value))))

Answer 3

只需使用defun*而不是defun(附带cl包).这个宏已就像Common Lisp中的defun(包装的函数体在try-catch块和别名return-from来throw等).

例如:

(require 'cl)

(defun* get-out-early ()
  "Get out early from this silly example."
  (when (not (boundp some-unbound-symbol))
    (return-from get-out-early))
  ;;
  ;; Get on with the func...
  ;;
  (do-such-and-such with-some-stuff))