negative subtraction

[Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>]

;;; -*- lexical-binding: t -*-
;;;
;;; this file:
;;;   http://user.it.uu.se/~embe8573/emacs-init/negative-subtraction.el
;;;   https://dataswamp.org/~incal/emacs-init/negative-subtraction.el

(require 'cl-lib)
(require 'parse-time)

(defun negative-subtract (a b)
  (let*((a-nums (number-to-list a))
        (b-nums (number-to-list b)) )
    (cl-loop
      for i in a-nums
      for j in b-nums
      collect (- i j) )))
;; (negative-subtract 8888 7777) ; (1 1 1 1)

(defun number-to-list (n)
  (cl-loop
    for d across (prin1-to-string n)
    collect (cl-digit-char-p d) ))
;; (number-to-list 1234) ; (1 2 3 4)

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