GNU bug report logs - #64584
29.0.91; skeleton: cannot pass `str' as argument to some functions

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From: Visuwesh <visuweshm <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 64584 <at> debbugs.gnu.org
Subject: bug#64584: 29.0.91; skeleton: cannot pass `str' as argument to some functions
Date: Tue, 12 Sep 2023 20:20:56 +0530

[செவ்வாய் செப்டம்பர் 12, 2023] Stefan Monnier wrote:

>> Yes, but here it basically does nothing unfortunately.  I am not sure if
>>
>>     'str
>>
>> should have the side effect of setting that variable.
>
> The above skeleton expression means "eval the variable `str` and throw
> away the result".  The only effect it can have is to signal an error if
> the variable `str` is not bound.

Ah yes, of course.  I am still thinking in vague terms of macroexpansion
which is leading to all the misunderstandings.

>>     (defmacro vz/snippet-when (form &rest body)
>>       "Evaluate BODY if FORM returns non-nil or non-empty string."
>>       (declare (indent 1) (debug (form body)))
>>       `(let ((str ,form))
>>          (if (and str (equal str ""))
>>              ""
>>            ,@body)))
>
> FWIW, this style of macro is usually called "anaphoric macro" and the
> convention is to use the identifier `it` rather than `str` in them.
> It would help avoid a confusion between skeleton's `str` and your
> macro's variable.

Oh yes, I called `it' first but changed it `str' "in anger".  So far, I
haven't been in the need of using both vz/snippet-when's `str' and
skeleton's `str' so I will let the sleeping dogs lie.

> [ And, yes, arguably, `define-skeleton` could be considered as an
>   anaphoric macro as well which should use `it` instead of `str`,
>   bringing back the confusion :-)  ]

I guess it wasn't chosen because there are other variables too (like
help, v1, v2, etc.).

I cannot think of any improvements to the documentation since the spawn
of this bug report is rooted in a lack of understanding of how skeleton
works.  There is nothing to fix here except my understanding so I'm
closing the bug report with this.  Thank you again for your time,
Stefan.

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