Re: ~`symbol-function' to get code as list even when byte-compiled?

[Barry Margolin]

In article <877frxid14.fsf@debian.uxu>,
 Emanuel Berg <embe8573@student.uu.se> wrote:

> (re-search-forward "^Question")
> 
> Here is some interesting code. What's interesting is:
> when this code executes, it changes itself, i.e.
> the code changes the code!
> 
> But it isn't a macro which is a program that produces
> a new program based on its own logic and non-evaluated
> input data.
> 
> On the contrary, here we deal all with ordinary
> functions (defuns) where one changes the other.
> Does that always happen? No - only when it is needed!
> 
> See the entire code here [1]. Go there if you want to
> see this in execution as it probably is based on some
> other functions as well. The below code is for display
> purposes ONLY!
> 
> Question: this is all working thanks to
> `symbol-function' which is used to get the code of the
> function as data, so it can be examined and
> manipulated. However, if I byte-compile the code
> (which I always do), `symbol-function' doesn't return
> a lambda function which is also a list, but instead
> just a function #[...] which isn't a list. So then it
> doesn't work!
> 
> I was able to do a workaround with `load-file' in
> .emacs to get all the functions in the file in
> evaluated form. But, can I do that specifically for
> a named function, *or*, can I extract the code in list
> format somehow even if compiled?

You can probably prevent it from being compiled, maybe something like:

(setf (symbol-function 'number-one-jump)
     '(lambda (&optional not-used) ...))

But can't you do something equivalent by using advice instead of 
self-modifying code?

> 
> (symbol-function jump)
> 
> (defun enable-jump (jump)
>   (add-hook 'w3m-display-hook jump)
>   (let*((code                  (symbol-function jump))
>         (remove-code           `(remove-hook 'w3m-display-hook (quote ,jump)))
>         (remove-code-index     2)
>         (current-code          (nth remove-code-index code)) )
>     (unless (equal current-code remove-code)
>       (push remove-code (nthcdr remove-code-index code)) )))
> 
> (defun web-search ()
>   (interactive)
>   (let ((search (get-search-string "Google")))
>     (unless (empty-string-p search)
>       (w3m-new-tab (format "Google: %s" search))
>       (w3m-search w3m-search-default-engine search) ))
>   (enable-jump 'number-one-jump) )
> 
> (defun number-one-jump (&optional not-used) ; Google, Youtube
>   (when (re-search-forward "^ 1." (point-max) t)
>     (recenter-top-bottom 0)
>     (w3m-next-anchor) ))
> 
> [1] http://user.it.uu.se/~embe8573/conf/emacs-init/w3m/w3m-unisearch.el

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***