4 ms·

Forbidden Emacs Lisp Knowledge: Block Comments

109 points by hprotagonist 5y ago

amno 5y ago
Nice! My two-minute thought on your idea, I refactored your code somewhat: ;;; test.el --- -*- lexical-binding: t; -*- Don't know if it's useful in practice, but if we had multiline comments, we could add invisible property on those markers to auto-hide them. Interlaced with Emacs Lisp code, it gives a "feel" of literate programming. (defun cursed-elisp-block-comment (beg end) (interactive "r") (save-excursion (let ((start (format "#@%d " (+ (- end beg) 2)))) (goto-char end) (insert "\037") (put-text-property end (1+ end) 'invisible t) (goto-char beg) ;; account for space and terminator (insert start) (put-text-property beg (+ beg (length start)) 'invisible t)))) (defun make-visible (beg end) (interactive "r") (remove-text-properties beg end '(invisible t))) This file is a little demo of the concept, but to actually be useful, there should probably be some routine to automatically mark text paragraphs with invisible markers, since it is a bit labourous to do it by hand for each paragraph. Surprisingly, indentation engine didn't complain at all, while font-lock of course does not know I am in a comment. (message "hello multiline comments") (provide 'test) ;;; test.el ends here Above file evaled as emacs-lisp buffer: https://postimg.cc/SnfNNfyh https://postimg.cc/SnfNNfyh
sillysaurusx 5y ago
I compiled my own emacs to expose internal-interpreter-environment or whatever it’s called. It’s roughly equivalent to the python locals() function. I have no idea why they thought it was a bad idea to expose, but it’s super handy. Also literally forbidden.
CyberShadow 5y ago
That's a cool find. On a practical note, at the top level or in the middle of progn-like constructs, you can do "block comments" with just: '( ... ) I.e., quote the form to prevent evaluating it.
- fiddlerwoaroof 5y ago
  I’ve always defined a `comment` macro that expands to nil. It works in most situations but it returns a value
  - dan-robertson 5y ago
    Reminds me of comments in MS batch files. I think there is just a program called REM (ie REMark, used to begin comments) which just ignores its arguments and immediately returns.
  - agumonkey 5y ago
    I always hesitate to return the commented expression or nil or '(:comment expr...) Nonetheless comment macros are neat. Just like #_(ignored) in clojure or else.
  - NoahTheDuke 5y ago
    Clojure has that built-in and it’s great. Works wonders when testing things too: write a small test in a comment block and you can edit/evaluate a function then move to the comment and see the result immediately.
    - fiddlerwoaroof 5y ago
      Yeah, that’s where I got the idea.

109 points by hprotagonist 5y ago

amno 5y ago

Nice! My two-minute thought on your idea, I refactored your code somewhat: ;;; test.el --- -*- lexical-binding: t; -*- Don't know if it's useful in practice, but if we had multiline comments, we could add invisible property on those markers to auto-hide them. Interlaced with Emacs Lisp code, it gives a "feel" of literate programming. (defun cursed-elisp-block-comment (beg end) (interactive "r") (save-excursion (let ((start (format "#@%d " (+ (- end beg) 2)))) (goto-char end) (insert "\037") (put-text-property end (1+ end) 'invisible t) (goto-char beg) ;; account for space and terminator (insert start) (put-text-property beg (+ beg (length start)) 'invisible t)))) (defun make-visible (beg end) (interactive "r") (remove-text-properties beg end '(invisible t))) This file is a little demo of the concept, but to actually be useful, there should probably be some routine to automatically mark text paragraphs with invisible markers, since it is a bit labourous to do it by hand for each paragraph. Surprisingly, indentation engine didn't complain at all, while font-lock of course does not know I am in a comment. (message "hello multiline comments") (provide 'test) ;;; test.el ends here Above file evaled as emacs-lisp buffer: https://postimg.cc/SnfNNfyh https://postimg.cc/SnfNNfyh

sillysaurusx 5y ago

I compiled my own emacs to expose internal-interpreter-environment or whatever it’s called. It’s roughly equivalent to the python locals() function. I have no idea why they thought it was a bad idea to expose, but it’s super handy. Also literally forbidden.

CyberShadow 5y ago

That's a cool find. On a practical note, at the top level or in the middle of progn-like constructs, you can do "block comments" with just: '( ... ) I.e., quote the form to prevent evaluating it.

fiddlerwoaroof 5y ago
I’ve always defined a `comment` macro that expands to nil. It works in most situations but it returns a value
- dan-robertson 5y ago
  Reminds me of comments in MS batch files. I think there is just a program called REM (ie REMark, used to begin comments) which just ignores its arguments and immediately returns.
- agumonkey 5y ago
  I always hesitate to return the commented expression or nil or '(:comment expr...) Nonetheless comment macros are neat. Just like #_(ignored) in clojure or else.
- NoahTheDuke 5y ago
  Clojure has that built-in and it’s great. Works wonders when testing things too: write a small test in a comment block and you can edit/evaluate a function then move to the comment and see the result immediately.
  - fiddlerwoaroof 5y ago
    Yeah, that’s where I got the idea.