How do you comment out all or part of a Lisp s-exp using Paredit?

When editing Lisp code, occasionally it's useful to entirely comment out a top-level definition, like this:

;(defun some-fn-which-is-broken (x)
;  ...)

... or comment out only part of an s-expression, like this:

(foo x
;    y
     z)

... and then recompile the file and test something in the REPL, etc.

Wit开发者_Go百科h paredit-mode enabled, this doesn't work. Here's what happens, if the point is right before the first paren below:

(defun some-fn (x)
  ...)

and you type a semicolon, what is entered is a semicolon and a newline:

;
(defun some-fn (x)
  ...)

Same with commenting out part of the s-expression:

(foo x
;    
     y
     z)

I think that if the definition is all on one line, this works:

;(defparameter *foo* 10)

... but otherwise I can't find out how to do this. Paredit is great, I would really like to keep using it. Are there any Lispers who know a way around this, or Emacs-wizards who can whip up a bit of Emacs Lisp to bind to something like paredit-comment-out-s-expr?

If there is a more Lispy or Emacsy way of accomplishing essentially the same thing, commenting out parts of source to recompile, please, don't hesitate to suggest them!

Position the point on the first character of the whole sexp, mark the whole sexp with C-M-space, and issue M-; to do the commenting. If it is necessary to do so, your source code will also be re-formatted so that only the sexp you marked, and nothing that was also on the same line, is in a comment.

You can very easily make a simple command or even a macro to do that:

(defun comment-sexp ()
  "Comment out the sexp at point."
  (interactive)
  (save-excursion
    (mark-sexp)
    (paredit-comment-dwim)))

Just a side note:

The #+ and #- reader macros are pretty nice for commenting out sexps. They allow ignoring the following sexp, if the given symbol isn't/is found in *FEATURES*. Just pick a symbol not in *FEATURES*, and use it with #+ like this:

#+nil
(defun foo ()
  ...)

Now, the function definition will be ignored (unless NIL is in *FEATURES*, which is not very likely).

As a stopgap measure, you can use C-q (quoted-insert) to insert an arbitrary character without triggering any mode-related magic. For example, in java-mode, typing parentheses reindents the current line, which is not always what I want; in such cases, I'll insert a parenthesis with C-q to preserve my indentation. (Or more often, I'll type a parenthesis, observe the indentation change, curse, undo, and re-enter with C-q.)

For commenting in general, it would probably be easier to use M-; (comment-dwim) rather than typing the semicolons manually.

You can use C-M-SPC M-; to mark the S-expression (C-M-SPC for mark-sexp) and then comment it (M-; for comment-dwim).

In paredit 23, just typing ; won't push anything it doesn't have to off the line. So it will do the right thing for your second example. And if you wanted to comment out z instead of y it would push only the closing delimiter to another line.