Function to add a number at the end of a line to another number on the top line

Question

I'm trying to implement a gamification system in org-mode.

Basically, I assign a number of points to a checkboxed task and when I tick the checkbox I add the number of points to a total at the top of my file.

I'm trying to write a function that does this automatically, like for example turning this:

Total points: 45

- Things to do today
  - [ ] Wa|sh clothes: 5

into this:

Total points: 50

- Things to do today
  - [X] Wa|sh clothes: 5

when the cursor is at the vertical bar.

How would I write a function that extracts the number from the end of the line and stores it in a variable, extracts the top number and stores it in a variable, adds the variables together and replaces the top number with the new total?

Answer 1

I found the answer to my own question - the trick was to use setq with thing-at-point to get the value into a variable:

(defun tally-adder ()
  "Adds local tally to global tally"
  (interactive)  
  (save-excursion
    (move-end-of-line nil)
    (setq end-of-line-tally (thing-at-point 'number))
    (beginning-of-buffer)
    (move-end-of-line nil)
    (setq global-tally (thing-at-point 'number))
    (backward-kill-word 1)
    (insert (number-to-string (+ end-of-line-tally global-tally)))))