;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/negative-subtraction.el

(require 'cl-lib)

(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)

(defun negative-subtract (a b)
  (let* ((an (number-to-list a))
         (bn (number-to-list b)))
    (cl-loop
      for i in an
      for j in bn
      collect (- i j))))

;; (negative-subtract 256 118) ; (1 4 -2)
;; (- 256 118) ; 138

(provide 'negative-subtraction)