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bug#68075: 30.0.50; New special form `handler-bind`
From: |
Stefan Monnier |
Subject: |
bug#68075: 30.0.50; New special form `handler-bind` |
Date: |
Thu, 28 Dec 2023 17:04:45 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) |
>> I'm trying to explain that when looking for a handler, we look both for
>> condition-case handler and handler-bind handlers and we use whichever is
>> "closest", i.e. more deeply nested. So just like a local
>> `condition-case` overrides temporarily an outer one, the same holds not
>> only among `handler-bind`s but also between `condition-case` and
>> `handler-bind` as well.
>
> Then, it would also make sense to make `condition-case' and
> `handler-bind' refer to each other from the docstrings.
BTW, `condition-case` can be implemented as a macro on top of
`handler-bind` and `catch`, e.g.
(condition-case ERR FORM (error HANDLER))
can become something like:
(let* ((tag (cons nil nil))
(ERR (catch tag
(handler-bind ((error (lambda (err) (throw tag err))))
(cons 'noerror FORM)))))
(if (eq 'noerror (car ERR))
(cdr ERR)
HANDLER))
:-)
-- Stefan