comment lines matching a regexp

comment-prints.el

(defun s-trim-left (s)
  "Remove whitespace at the beginning of S."
  (if (string-match "\\`[ \t\n\r]+" s)
      (replace-match "" t t s)
    s))

(defun first-word (s)
  (let ((s-trim (s-trim-left s)))
    (car (split-string s-trim " "))))

(defun get-lines-of-buffer (buff what-to-do)
  (with-current-buffer buff
  ;;(save-excursion)
  (setq start-char 1)
  (while (< start-char (point-max))
    (goto-char start-char)
    (let* ((end-line (line-end-position))
           (tmp-str (buffer-substring-no-properties (line-beginning-position) end-line)))
      (funcall what-to-do tmp-str)
      (setq start-char (+ 1 end-line))))))


(defun get-nth-char (s n)
  (substring s n (+ 1 n)))

(defun get-count-spaces (str)
  (progn
    (setq n 0)
    (while (and (string= " " (get-nth-char str n)) (< n (string-width str)))
      (setq n (+ 1 n)))
    n))

(defun comment-prints ()
  (interactive)
  (save-excursion
    (get-lines-of-buffer
     (current-buffer)
     (lambda (str)
       (when
           (string= "print" (first-word str))
         (goto-char (+ (line-beginning-position) (get-count-spaces str)))
         (insert "#" )) ))))