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;;; eval-sexp-in-comments.el --- evaluate sexps in comments

;; Copyright (C) 2001  Alex Schroeder

;; Emacs Lisp Archive Entry
;; Filename: eval-sexp-in-comments.el
;; Version: 1.0.0
;; Keywords: lisp
;; Author: Alex Schroeder 
;; Maintainer: Alex Schroeder 
;; Created: 2001-01-07
;; Description: evaluate sexps in comments
;; URL: http://www.geocities.com/kensanata/emacs.html
;; Compatibility: Emacs20, XEmacs21

;; `eval-last-sexp-in-comments' attempts to evaluate the last sexp using
;; `eval-last-sexp' (the latter usually being on C-x C-e).  If that
;; raises an error, however, `eval-last-sexp-in-comments' will try to
;; uncomment the last sexp in a temporary buffer and evaluate
;; `eval-last-sexp' there.  This is usefull when you have commented
;; debugging code in you elisp files, which you want to use.  Instead of
;; uncommenting the region, hitting C-x C-e, and commenting the stuff
;; again when you are done, just redefine C-x C-e, such that
;; `eval-last-sexp-in-comments' is called instead of `eval-last-sexp'.

;; Test by evaluating all the following expressions while they are
;; commented.  Some of them are supposed to work, others not.

;; (let ((str "Commented sexp works"))
;;    (message str))
;; (let ((str "Commented sexp works with nested comment"))
;;    ;; nested comment!
;;    (message str))
;; (let ((str "Commented sexp works with empty commented lines"))
;;
;;    (message str))
;; (let ((str "This does not work due to garbage"))
;;    garbage!
;;    (message str))
; (let ((str "This does not work due to different indentation"))
;;    (message str))
;;; (let ((str "This does not work due to different indentation"))
;;    (message str))

(defun eval-last-sexp-in-comments (stuff)
  "Evaluate sexp before point; print value in minibuffer.
With argument, print output into current buffer.
This works even if the sexp before point is commented out."
  (interactive "P")
  (condition-case var
      (eval-last-sexp stuff)
    (error
     (save-excursion
       (let ((start (point))
	     end comment-intro str)
	 (setq end (progn
		     (beginning-of-line)
		     (if (not (looking-at "^\\s *;+"))
			 (signal (car var) (cdr var))
		       (setq comment-intro (concat "^" (match-string 0) "[^;]"))
		       (while (and (forward-line -1)
				   (looking-at comment-intro)))
		       (if (not (looking-at comment-intro))
			 (forward-line 1))
		       (point)))
	       str (buffer-substring-no-properties start end))
	 (with-temp-buffer
	   (insert str)
	   (message str)
	   (goto-char (point-min))
	   (while (re-search-forward comment-intro nil t)
	     (replace-match ""))
	   (goto-char (point-max))
	   (eval-last-sexp stuff)))))))

(define-key emacs-lisp-mode-map (kbd "C-x C-e") 'eval-last-sexp-in-comments)