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bug#25154: 25.1; Bindings in cl-letf are in reverse order


From: npostavs
Subject: bug#25154: 25.1; Bindings in cl-letf are in reverse order
Date: Sat, 10 Dec 2016 13:14:54 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)

Alex <address@hidden> writes:

>>
>> Isn't it true that the order of evaluation in a 'let' is unspecified?
>> If you want a particular order, use 'let*'.
>
> I don't think so. See (info "(elisp) Local Variables"):
>
>   All of the VALUE-FORMs in BINDINGS are evaluated in the order they
>   appear
>
> I believe it should follow for cl-letf. Besides, even if it was
> unspecified, evaluating in the order they appear would be adhering to
> the principle of least astonishment.

The value forms are evaluated in order, the bindings are not necessarily
in order.

(let ((x 0))
  (cl-letf ((a (setq x 1))
            (a (setq x 2)))
    (list x a))) ;=> (2 1)

Although `let' does happen to perform the bindings in order too.

(let ((x 0))
  (let ((a (setq x 1))
        (a (setq x 2)))
    (list x a))) ;=> (2 2)





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