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

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> 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.

>     (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.

[ 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 :-)  ]


        Stefan