;;
;;  Hide specific "sections"
;;  2011.11.19. Toshi Nagata
;;
(defun LilyPond-hide-sections (str)
  (interactive "sSections to hide (like 1,2,3 or 1-3): ")
  (let (sections-to-hide last-section next-section last-pos next-pos has-brace)
    ;; Get a list of sections to hide
    (setq sections-to-hide
	  (apply
	   'append
	   (mapcar
	    (lambda (s)
	      (if (string-match "^\\([0-9]+\\)-\\([0-9]+\\)$" s)
		  (let ((n1 (string-to-number (match-string 1 s)))
			(n2 (string-to-number (match-string 2 s))))
		    (if (<= n1 n2)
			(let ((ls nil))
			  (while (<= n1 n2)
			    (setq ls (cons n2 ls))
			    (setq n2 (- n2 1)))
			  ls)
		      nil))
		(list (string-to-number s))))
	    (split-string str ","))))
    (save-excursion
      ;; Unhide all sections
      ;; }?%{ [n] ... % [m] %} -> % [n] ... % [m]
      (goto-char (point-min))
      (while (re-search-forward "^\\(}?\\)%{ \\[[0-9]+\\]" nil t)
	(setq last-pos (match-beginning 0))
	(setq has-brace (equal (match-string 1) "}"))
	(cond ((re-search-forward "^% \\[[0-9]+\\] %}" nil t)
	       (delete-char -3)
	       (beginning-of-line)
	       (setq next-pos (- (point) 1))
	       (goto-char last-pos)
	       (cond (has-brace
		      (delete-char 1)
		      (setq next-pos (- next-pos 1))))
	       (forward-char 1)
	       (delete-char 1)
	       (end-of-line)
	       (forward-char 1)
	       (uncomment-region (point) next-pos))))
      ;; Hide specified sections
      (goto-char (point-min))
      (setq last-section nil)
      (while (re-search-forward "^% \\[\\([0-9]+\\)\\]" nil t)
	(setq next-section (string-to-number (match-string 1)))
	(cond ((member next-section sections-to-hide)
	       ;;  This section is to be hidden
	       (cond ((or (not last-section) (>= last-section next-section))
		      ;;  The beginning section - record as last-section
		      (setq last-pos (match-beginning 0))
		      (setq last-section next-section))
		     (t
		      ;;  Otherwise, just wait until the end section comes
		      nil)))
	      (t
	       ;;  This section is not to be hidden
	       (cond ((and last-section (< last-section next-section))
		      ;;  Hide last-section up to here
		      (insert " %}")
		      (beginning-of-line)
		      (setq next-pos (+ (point) 1))
		      (goto-char last-pos)
		      (forward-char 1)
		      (insert "{")
		      (end-of-line)
		      (cond ((eq (preceding-char) ?\{)
			     ;; % [n]  .... {\n  -> }%{ [n]  .... {\n
			     (beginning-of-line)
			     (insert "}")
			     (end-of-line)
			     (setq next-pos (+ next-pos 1))))
		      (setq last-pos (+ (point) 1))
		      (comment-region last-pos next-pos)
		      (end-of-line)))
	       (setq last-section nil)))))))