Elisp version of CL: (format t "~:d" NUM)

[Jean Louis <bugs@gnu.support>]

In Common Lisp it is very easy to get readable comma separated digits:

(clisp-macro (format t "~:d" 123456890)) ⇒ "123,456,890"

As from:
http://www.lispworks.com/documentation/HyperSpec/Body/22_cbb.htm

In Emacs Lisp I have made this below, did not tested it much yet. And
I think this function is way too big. Maybe there is some simpler way?

(defun number-comma-char (num)
  "For NUM return readable comma separated digits."
  (let* ((num (cond ((numberp num) (number-to-string num))
		    (t num)))
	 (decimal (string-match "\\." num))
	 (rest (if decimal (substring num decimal) ""))
	 (num (if decimal (substring num 0 decimal) num))
	 (count 1)
	 (list)
	 (chain (seq-map 'identity (reverse num))))
    (while chain
      (let ((char (pop chain)))
	(cond ((and (= (truncate (/ count 3.0)) (/ count 3.0))
		    chain)
	       (progn
		 (push char list)
		 (push ?, list)))
	      (t (push char list)))
	(setq count (1+ count))))
    (concat (mapconcat 'char-to-string list "") rest)))

(number-comma-char 123456.0) ⇒ "123,456.0"



Jean

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