Xah Talk Show 2021-05-17 Emacs Lisp Live Coding. Convert MM:SS to Seconds and Reverse

links mentioned:

• Emacs Lisp Basics
• Elisp: Using thing-at-point
• Elisp: Syntax Table
• Unicode for Programers
• Unicode: Character Set, Encoding, UTF-8, Codepoint
• unicode character categorization http://www.unicode.org/notes/tn36/
• Unicode: Cultural Religious Symbols 💀
• Unicode: Chinese 中文
• JS: RegExp Unicode Property
• Emacs: Xah Math Input Mode

(defun convertSecondsToMinSecs ()
  "Convert seconds to mm:ss format, or vice versa, on current word.
If the current word contains a colon, then do the reverse direction conversion.
Version 2021-05-17"
  (interactive)
  (let (boundaryX p1 p2 wordX totalSecondsX minuteX secsX listX )
    (save-excursion
      (search-backward " " )
      (forward-char 1)
      (setq p1 (point))
      (search-forward " " )
      ;; (re-search-forward "[ \n]" )
      (backward-char 1)
      (setq p2 (point)))
    (setq wordX (buffer-substring-no-properties p1 p2))
    (if (string-match ":" wordX )
        (progn
          (setq listX (split-string wordX ":" ))
          (setq minuteX (string-to-number (nth 0 listX)))
          (setq secsX (string-to-number (nth 1 listX)))
          (delete-region p1 p2)
          (insert (format "%s" (+ (* minuteX 60) secsX))))
      (progn
        (setq totalSecondsX (string-to-number wordX))
        (setq minuteX  (/ totalSecondsX 60))
        (setq secsX (% totalSecondsX 60))
        (delete-region p1 p2)
        (insert (format "%s:%s" minuteX secsX ))))))