12

I need to call a function and perform a cleanup only if the function fails, and then relaunch the error. Here is the pseudo-code:

(condition-case err
    (call-function)
  (error
   (cleanup)
   ;; how do I raise `err`?
   ))
Malabarba
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Eleno
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2 Answers2

16

You're looking for signal:

(condition-case err
    (call-function)
  (error
   (cleanup)
   (signal (car err) (cdr err)))) ; reraise `err'
npostavs
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12

BTW, an alternative option can be something like:

(let ((error t))
  (unwind-protect
      (prog1 (call-function)
        (setq error nil))
    (when error (cleanup))))

The advantage is that you avoid catching&rethrowing the error, which means for example that the debugger will show you the right backtrace (the one that corresponds to the actual source of the error, rather than the one that corresponds to you re-throwing someone else's error).

Another differences is that cleanup will be called not only upon error but also if the code is interrupted by a C-g or a call to throw.

Stefan
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    Thanks. Why wouldn't condition-case catch keyboard-quit? – Eleno Jul 08 '15 at 07:02
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    Because it's not an error (i.e. its signal, quit, does not have error among its parents). IOW you van also catch it with condition-case but for that you need to put quit along with error. Of course, that still won't handle the `throw' case. – Stefan Jul 08 '15 at 13:41
  • +1 For many common cases, unwind-protect is a neater alternative to fine-grained exception handling with condition-case. – mindthief Nov 23 '20 at 03:02