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Subject: |
28.0.50; A problem with rx-let expansion |
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Date: |
Fri, 20 Aug 2021 15:59:44 +0200 |
Hello,
I'm referring to this paragraph in rx.el:
;; FIXME: Consider adding extensions in Lisp macro style, where
;; arguments are passed unevaluated to code that returns the rx form
;; to use.
;; [...]
;; While this would permit more powerful extensions, it's unclear just
;; how often they would be used in practice. Let's wait until there is
;; demand for it.
Ok - here is! I would find that approach much more natural than the
current one. Look:
Already the first `rx-let' pseudo macro I tried hit a problem (bug) with
the current approach:
#+begin_src emacs-lisp
(rx-let ((scatter (string)
(regex (mapconcat #'string (string-to-list string) ".*"))))
(rx (scatter "abc"))) => useless error message
#+end_src
while the following version (the only difference is the argument name)
works as expected:
#+begin_src emacs-lisp
(rx-let ((scatter (s) (regex (mapconcat #'string (string-to-list s) ".*"))))
(rx (scatter "abc"))) ==> "a.*b.*c"
#+end_src
Seems the function form #'string gets replaced and ends as #'"abc" in
the first version because the function name accidentally collides with
the argument name.
Personally I would be more happy with a thing called `rx-macrolet' than
with an extended `rx-let' to support this additional macro-like kind of
syntax.
TIA,
Michael.
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Subject: |
Re: 28.0.50; A problem with rx-let expansion |
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Date: |
Mon, 23 Aug 2021 20:05:26 +0200 |
23 aug. 2021 kl. 18.59 skrev Michael Heerdegen <michael_heerdegen@web.de>:
> Maybe at least one sentence about that this mechanism just performs
> trivial substitution?
I didn't do that now, because I couldn't see how it could be interpreted
otherwise (and there's the manual link).
> I find the term "user-defined" distracting, because anybody (including
> library and package developers) is "affected". Apart from that, ok for
> me.
Thank you, changed.
> Didn't try the example, but it looks good.
Thanks for looking at it. Good examples are always hard to write!
> | (eval EXPR) Match the rx sexp from evaluating EXPR at compile time.
>
> can we say "expansion time" instead of "compile time"?
We can, and now do!
Closing; I think we're done here (complain if not).
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