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Re: A couple rudimentary elisp questions
From: |
exits funnel |
Subject: |
Re: A couple rudimentary elisp questions |
Date: |
Tue, 2 Mar 2004 13:40:05 -0800 (PST) |
> In emacs lisp there's no multiline comment. You can
> use
> comment-region / uncomment-region to comment several
> lines at once.
>
> Otherwise you can use this trick: use a multi-line
> string as a
> comment, like you do for documentation strings:
>
> (defun my-fun ()
> " This
> is the documentation
> string of the function
> my-fun that appears
> when you ask for the
> function documentation
> with (describe-function 'my-fun)
> or C-h C-f my-fun RET
> "
> (do-something)
> " Here is a ''comment''
> spread on several
> lines.
> Actually, it's not a
> comment, it's a string
> that is ''evaluated''
> in the course of this
> function, but since
> we don't do anything
> with it, it's finally
> ignored. "
> (do-something-else)
> (get-result))
>
> Of course, since the strings are syntactically
> significant, you must
> take care where you put them. You can't put them
> inside function
> argument lists, or inside other data lists. They
> eventually get
> ignored only in statement lists, inside progn and
> equivalent (and not
> in a result position!).
>
> Perhaps a cleaner way to do it would be to defined a
> comment macro:
>
> (defmacro rem (&rest args))
>
> (defun my-fun ()
> " This
> is the documentation
> string of the function
> my-fun that appears
> when you ask for the
> function documentation
> with (describe-function 'my-fun)
> or C-h C-f my-fun RET
> "
> (do-something)
> (rem Here we have a "comment"
> but it is still scanned
> and tokenized.
> "So we may still use strings
> and use any kind of invalid
> token such as . . . :-)
> But note that you must still
> escape double-quotes such as: \"
> ")
> (do-something-else)
> (get-result))
>
> You get two advantages with this rem macro:
>
> 1- a code walker can find your comments if you
> need to process them.
>
> 2- since the macro generates nothing, the
> comment/strings don't
> eventually appear in compiled code, and the
> execution of
> compiled code is strictly equivalent with or
> without the (rem ...)
> (that could be not the case without the
> macro).
> It's the notation for a cons cell:
>
> (cons 'foo 'bar) == (foo . bar)
>
> Lists are built on cons cells, starting from the
> empty list ():
>
> (cons 'foo ()) == (foo . ())
> == (foo)
>
> (cons 'bar (cons 'foo ())) == (bar . (foo . ()))
> == (bar foo)
>
> (cons 'baz
> (cons 'bar
> (cons 'foo ()))) == (baz . (bar . (foo .
> ()))) == (baz bar foo)
>
>
> The value assigned to the symbol nil is (), the
> empty list, which is
> actually a special atom.
> The empty list () is NOT a cons: (consp ()) == nil,
> (atom ()) == t.
Pascal, I just wanted to take a quick moment to thank
you for your detailed reply. All of the information
was very helpful.
-exits
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