Re: (*) -> 1

[Tassilo Horn]

Jean Louis <bugs@gnu.support> writes:

> You found examples I am searching, though you can't provide references
> where (*) is useful.

Gosh, Jean, of course nobody would literally write (*) but (apply #'*
...), and you'll find occurrences in emacs:

--8<---------------cut here---------------start------------->8---
find -H . -type d \( -path \*/SCCS -o -path \*/RCS -o -path \*/CVS -o
-path \*/MCVS -o -path \*/.src -o -path \*/.svn -o -path \*/.git -o
-path \*/.hg -o -path \*/.bzr -o -path \*/_MTN -o -path \*/_darcs -o
-path \*/\{arch\} \) -prune -o \! -type d \( -name .\#\* -o -name
\*.out -o -name \*.synctex.gz -o -name \*.o -o -name \*\~ -o -name
\*.bin -o -name \*.lbin -o -name \*.so -o -name \*.a -o -name \*.ln -o
-name \*.blg -o -name \*.bbl -o -name \*.elc -o -name \*.lof -o -name
\*.glo -o -name \*.idx -o -name \*.lot -o -name \*.fmt -o -name \*.tfm
-o -name \*.class -o -name \*.fas -o -name \*.lib -o -name \*.mem -o
-name \*.x86f -o -name \*.sparcf -o -name \*.dfsl -o -name \*.pfsl -o
-name \*.d64fsl -o -name \*.p64fsl -o -name \*.lx64fsl -o -name
\*.lx32fsl -o -name \*.dx64fsl -o -name \*.dx32fsl -o -name \*.fx64fsl
-o -name \*.fx32fsl -o -name \*.sx64fsl -o -name \*.sx32fsl -o -name
\*.wx64fsl -o -name \*.wx32fsl -o -name \*.fasl -o -name \*.ufsl -o
-name \*.fsl -o -name \*.dxl -o -name \*.lo -o -name \*.la -o -name
\*.gmo -o -name \*.mo -o -name \*.toc -o -name \*.aux -o -name \*.cp -o
-name \*.fn -o -name \*.ky -o -name \*.pg -o -name \*.tp -o -name \*.vr
-o -name \*.cps -o -name \*.fns -o -name \*.kys -o -name \*.pgs -o
-name \*.tps -o -name \*.vrs -o -name \*.pyc -o -name \*.pyo \) -prune
-o  -type f \( -iname \*.el \) -exec grep --color=auto -i -nH --null -e
\(apply\ \#\'\\\* \{\} +
./gnus/spam-stat.el:494:         (prod (apply #'* probs))
./gnus/spam-stat.el:496:          (/ prod (+ prod (apply #'* (mapcar (lambda 
(x) (- 1 x))
./org/org-plot.el:232:    (apply #'* (org--plot/nice-frequency-pick 
weighted-factors))))
./org/org-plot.el:259:            (< (* (apply #'* f-pick) 2-val) 30))
./org/org-plot.el:262:            (< (* (apply #'* f-pick) 3-val) 30))
./htmlfontify.el:1055:    (let ((n (apply #'* m)))
--8<---------------cut here---------------end--------------->8---

And even more with (apply #'+ ...):

--8<---------------cut here---------------start------------->8---
find -H . -type d \( -path \*/SCCS -o -path \*/RCS -o -path \*/CVS -o
-path \*/MCVS -o -path \*/.src -o -path \*/.svn -o -path \*/.git -o
-path \*/.hg -o -path \*/.bzr -o -path \*/_MTN -o -path \*/_darcs -o
-path \*/\{arch\} \) -prune -o \! -type d \( -name .\#\* -o -name
\*.out -o -name \*.synctex.gz -o -name \*.o -o -name \*\~ -o -name
\*.bin -o -name \*.lbin -o -name \*.so -o -name \*.a -o -name \*.ln -o
-name \*.blg -o -name \*.bbl -o -name \*.elc -o -name \*.lof -o -name
\*.glo -o -name \*.idx -o -name \*.lot -o -name \*.fmt -o -name \*.tfm
-o -name \*.class -o -name \*.fas -o -name \*.lib -o -name \*.mem -o
-name \*.x86f -o -name \*.sparcf -o -name \*.dfsl -o -name \*.pfsl -o
-name \*.d64fsl -o -name \*.p64fsl -o -name \*.lx64fsl -o -name
\*.lx32fsl -o -name \*.dx64fsl -o -name \*.dx32fsl -o -name \*.fx64fsl
-o -name \*.fx32fsl -o -name \*.sx64fsl -o -name \*.sx32fsl -o -name
\*.wx64fsl -o -name \*.wx32fsl -o -name \*.fasl -o -name \*.ufsl -o
-name \*.fsl -o -name \*.dxl -o -name \*.lo -o -name \*.la -o -name
\*.gmo -o -name \*.mo -o -name \*.toc -o -name \*.aux -o -name \*.cp -o
-name \*.fn -o -name \*.ky -o -name \*.pg -o -name \*.tp -o -name \*.vr
-o -name \*.cps -o -name \*.fns -o -name \*.kys -o -name \*.pgs -o
-name \*.tps -o -name \*.vrs -o -name \*.pyc -o -name \*.pyo \) -prune
-o  -type f \( -iname \*.el \) -exec grep --color=auto -i -nH --null -e
\(apply\ \#\'\+ \{\} +
./leim/quail/hangul.el:341:    (if (zerop (apply #'+ (append hangul-queue nil)))
./leim/quail/hangul.el:353:  (if (not (zerop (apply #'+ (append hangul-queue 
nil))))
./net/newst-backend.el:2186:  (apply #'+
./net/imap.el:1810:     (apply #'+ (mapcar #'imap-body-lines body)))
./net/shr.el:2350:    (let ((extra (- (apply #'+ (append suggested-widths nil))
./net/shr.el:2351:                    (apply #'+ (append widths nil))
./treesit.el:2608:          (eq 0 (apply #'+ (mapcar #'treesit-node-child-count 
children))))
./textmodes/texinfmt.el:2044:            (apply #'+ 
texinfo-multitable-width-list))))
./gnus/gnus-picon.el:217:                 (setq len (apply #'+ (mapcar (lambda 
(x)
./gnus/gnus-cache.el:889:         (apply #'+ entry)
./gnus/gnus-score.el:2560:               (apply #'+ (mapcar
./gnus/gnus-sum.el:3836:            (apply #'+ (mapcar
./gnus/gnus-sum.el:8840:               (apply #'+ (mapcar 
#'gnus-summary-limit-children
./gnus/gnus-agent.el:4139:        (apply #'+ entry)
./gnus/spam-stat.el:515:      (apply #'+ scores))))
./calendar/solar.el:753:                (apply #'+
./calendar/solar.el:941:         (S (apply #'+ (mapcar (lambda(x)
./calendar/todo-mode.el:3697:  (mapcar (lambda (i) (apply #'+ (mapcar (lambda 
(x) (aref (cdr x) i))
./ses.el:625:   ses--linewidth  (apply #'+ -1 (mapcar #'1+ widths))
./ses.el:4037:  (apply #'+ (apply #'ses-delete-blanks args)))
./ses.el:4044:  (/ (float (apply #'+ list)) (length list)))
./org/org-plot.el:246:     (let* ((total-count (apply #'+ (mapcar #'cdr 
frequencies)))
./org/org-colview.el:1261:  (format (or printf "%s") (apply #'+ (mapcar 
#'string-to-number values))))
./org/org-colview.el:1265:  (format "%.2f" (apply #'+ (mapcar 
#'string-to-number values))))
./org/org-colview.el:1306:        (/ (apply #'+ (mapcar #'string-to-number 
values))
./org/org-colview.el:1324:   (lambda (&rest values) (/ (apply #'+ values) 
(float (length values))))
./org/org-colview.el:1340:   (/ (apply #'+ (mapcar 
#'org-columns--age-to-minutes ages))
./org/org-clock.el:2626:         (total-time (apply #'+ (mapcar #'cadr tables)))
./minibuffer.el:2025:                                   (apply #'+ (mapcar 
#'string-width s))
./minibuffer.el:2068:                                           (apply #'+ 
(mapcar #'string-width str))
./pcomplete.el:943:          (let* ((envpos (apply #'+ (mapcar #' length 
strings)))
./progmodes/cc-guess.el:368:                             (apply #'+
./progmodes/sql.el:3639:          (apply #'+ (mapcar (lambda (ch) (if (eq ch 
?\n) 1 0))
./progmodes/vhdl-mode.el:7480:          (apply #'+ (mapcar #'vhdl-get-offset 
syntax)))
./obsolete/thumbs.el:207:           (dirsize (apply #'+ (mapcar (lambda (x) 
(cadr x)) files-list))))
./obsolete/landmark.el:1428:  (apply #'+
./emacs-lisp/memory-report.el:254:    (apply #'+
./emacs-lisp/bytecomp.el:4515:    (let ((nvalues (apply #'+ (mapcar (lambda 
(case) (length (car case)))
./emacs-lisp/smie.el:2219:        (cl-assert (= total (apply #'+ (mapcar #'cdr 
off-alist))))
--8<---------------cut here---------------end--------------->8---

It's totally sensible to be able to compute the product/sum of an
arbitrary number of numbers.

All these would need checks for non-empty lists or even lists of at
least 2 numbers if + and * would require at least 1 or 2 arguments.

Bye,
Tassilo