GNU bug report logs - #66509
29.1.50; let-alist should support numeric indexing

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From: Artur Malabarba <arturmalabarba <at> gmail.com>
To: Stefan Kangas <stefankangas <at> gmail.com>
Cc: Spencer Baugh <sbaugh <at> janestreet.com>, 66509 <at> debbugs.gnu.org
Subject: bug#66509: 29.1.50; let-alist should support numeric indexing
Date: Mon, 16 Sep 2024 23:07:33 -0300

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Hi all,

The patch looks good.
Stefan, would you mind applying it? (It'll take a while for me to get
everything configured.)

best,
Artur


On Tue, 10 Sept 2024 at 20:22, Stefan Kangas <stefankangas <at> gmail.com> wrote:

> Artur, do you have any thoughts on the below patch?
>
> Spencer Baugh <sbaugh <at> janestreet.com> writes:
>
> > From 28e52a343f72dddd991cafd23fea910cc5f64ac5 Mon Sep 17 00:00:00 2001
> > From: Spencer Baugh <sbaugh <at> janestreet.com>
> > Date: Thu, 12 Oct 2023 18:01:46 -0400
> > Subject: [PATCH] Support numeric indexing in let-alist
> >
> > let-alist is very useful.  But sometimes an alist contains a list in
> > the middle, which contains yet more alists.  Previously, this was
> > somewhat painful to deal with, and required something like:
> >
> > (let-alist alist
> >   (let-alist (nth 0 .a)
> >     (let-alist (nth 3 .b)
> >        .c)))
> >
> > Now, the following works:
> >
> > (let-alist alist
> >   .a.0.b.3.c)
> >
> > * lisp/emacs-lisp/let-alist.el (let-alist--access-sexp): Properly
> > parse numbers.
> > (let-alist--list-to-sexp): Use nth to handle numbers.
> > (let-alist): Update docs.
> > ---
> >  lisp/emacs-lisp/let-alist.el | 25 +++++++++++++++----------
> >  1 file changed, 15 insertions(+), 10 deletions(-)
> >
> > diff --git a/lisp/emacs-lisp/let-alist.el b/lisp/emacs-lisp/let-alist.el
> > index d9ad46b2af7..de7c087bf2a 100644
> > --- a/lisp/emacs-lisp/let-alist.el
> > +++ b/lisp/emacs-lisp/let-alist.el
> > @@ -36,22 +36,23 @@
> >  ;; symbol inside body is let-bound to their cdrs in the alist.  Dotted
> >  ;; symbol is any symbol starting with a `.'.  Only those present in
> >  ;; the body are let-bound and this search is done at compile time.
> > +;; A number will result in a list index.
> >  ;;
> >  ;; For instance, the following code
> >  ;;
> >  ;;   (let-alist alist
> > -;;     (if (and .title .body)
> > +;;     (if (and .title.0 .body)
> >  ;;         .body
> >  ;;       .site
> >  ;;       .site.contents))
> >  ;;
> >  ;; essentially expands to
> >  ;;
> > -;;   (let ((.title (cdr (assq 'title alist)))
> > +;;   (let ((.title.0 (nth 0 (cdr (assq 'title alist))))
> >  ;;         (.body  (cdr (assq 'body alist)))
> >  ;;         (.site  (cdr (assq 'site alist)))
> >  ;;         (.site.contents (cdr (assq 'contents (cdr (assq 'site
> alist))))))
> > -;;     (if (and .title .body)
> > +;;     (if (and .title.0 .body)
> >  ;;         .body
> >  ;;       .site
> >  ;;       .site.contents))
> > @@ -93,14 +94,17 @@ let-alist--access-sexp
> >      (if (string-match "\\`\\." name)
> >          clean
> >        (let-alist--list-to-sexp
> > -       (mapcar #'intern (nreverse (split-string name "\\.")))
> > +       (mapcar #'read (nreverse (split-string name "\\.")))
> >         variable))))
> >
> >  (defun let-alist--list-to-sexp (list var)
> >    "Turn symbols LIST into recursive calls to `cdr' `assq' on VAR."
> > -  `(cdr (assq ',(car list)
> > -              ,(if (cdr list) (let-alist--list-to-sexp (cdr list) var)
> > -                 var))))
> > +  (let ((sym (car list))
> > +        (rest (if (cdr list) (let-alist--list-to-sexp (cdr list) var)
> > +                 var)))
> > +    (cond
> > +     ((numberp sym) `(nth ,sym ,rest))
> > +     (t `(cdr (assq ',sym ,rest))))))
> >
> >  (defun let-alist--remove-dot (symbol)
> >    "Return SYMBOL, sans an initial dot."
> > @@ -116,22 +120,23 @@ let-alist
> >    "Let-bind dotted symbols to their cdrs in ALIST and execute BODY.
> >  Dotted symbol is any symbol starting with a `.'.  Only those present
> >  in BODY are let-bound and this search is done at compile time.
> > +A number will result in a list index.
> >
> >  For instance, the following code
> >
> >    (let-alist alist
> > -    (if (and .title .body)
> > +    (if (and .title.0 .body)
> >          .body
> >        .site
> >        .site.contents))
> >
> >  essentially expands to
> >
> > -  (let ((.title (cdr (assq \\='title alist)))
> > +  (let ((.title (nth 0 (cdr (assq \\='title alist))))
> >          (.body  (cdr (assq \\='body alist)))
> >          (.site  (cdr (assq \\='site alist)))
> >          (.site.contents (cdr (assq \\='contents (cdr (assq \\='site
> alist))))))
> > -    (if (and .title .body)
> > +    (if (and .title.0 .body)
> >          .body
> >        .site
> >        .site.contents))
>

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