Re: cond*

[Ihor Radchenko <yantar92@posteo.net>]

Richard Stallman <rms@gnu.org> writes:

>   > Other than rx, one missing feature is an ability to match against
>   > multiple values in a single condition:
>   > (defun yant/list-sum (list)
>   >   (apply #'+ list))
>   > (pcase '(1 2 3)
>   >   ((and `(,x ,y ,z) (app yant/list-sum (and sum (guard (< 2 sum)))))
>   >    (format "%d + %d + %d = %d; 2 is < %d" x y z sum sum)))
>   > ; => "1 + 2 + 3 = 6; 2 is < 6"   
>
> Understanding this was a struggle, but I think it can be done with
>
>   (cond* ((match* `(,x ,y ,z) list-of-three))
>          ((< 2 (+ x y z))
>           success)))

Nope.

Consider

(let ((list-of-three '(1 2)))
  (cond* ((match* `(,x ,y ,z) list-of-three))
         ((< 2 (+ x y z))
          'success))) ; => (wrong-type-argument number-or-marker-p nil)

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  (+ 1 2 nil)
  (< 2 (+ x y z))
  (if (< 2 (+ x y z)) (progn 'success))
  (let* ((z (nth 2 d2495))...

I used the latest version of cond* you submitted in
https://yhetil.org/emacs-devel/86cytg1vcu.fsf@gnu.org/T/#t

Also, I was surprised by

(let ((list-of-three '(1 2 3 4)))
  (cond* ((match* `(,x ,y ,z) list-of-three))
         ((< 2 (+ x y z))
          'success))) ; => success

I did not expect list of four to match `(,x ,y ,z).

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>