Xah Talk Show 2022-03-04 emacs lisp coding and tutorial. swap/transpose text blocks

focused emacs lisp coding and tutorial. a command to swap current text block with previous. no random topic.

• emacs lisp write xah-transpose-block

• Elisp: Get Text Block 🚀
• Notes on A New Kind of Science
• Wolfram Language Tutorial

• transpose-chars
• transpose-lines
• transpose-paragraphs
• transpose-regions
• transpose-sentences
• transpose-sexps
• transpose-words

(defun xah-transpose-block ()
  "swap the current text block with the previous.
Version 2022-03-04"
  (interactive)
  (let (($curCursPos (point))
        $c1 ; current block begin
        $c2 ; current Block End
        $p1 ; prev Block Begin
        $p2 ; prev Block end
        )

    (save-excursion
      (if (re-search-forward "\n[ \t]*\n+" nil "move")
          (setq $c2 (match-beginning 0))
        (setq $c2 (point)))

      (goto-char $curCursPos)

      (if (re-search-backward "\n[ \t]*\n+" nil "move")
          (progn
            (setq $c1 (match-end 0))
            (skip-chars-backward "\n \t")
            (setq $p2 (point)))
        (error "No previous block."))

      (goto-char $p2)

      (if (re-search-backward "\n[ \t]*\n+" nil "move")
          (setq $p1 (match-end 0))
        (setq $p1 (point)))

      (transpose-regions $p1 $p2 $c1 $c2)))
  ;;
  )

(global-set-key (kbd "C-d") 'xah-transpose-block)

• xah_talk_show_2022-03-04.txt