Re: [O] using flet to suppress meta generation in html export?

[Matt Price]

AH, THISI S SUPER-HELPFUL, aARON. MANY THANK.  i'M HOPING THAT BY THE TIME i RETIRE i WILL BEGIN TO UNDERSTAND LEXICAL SCOPING IN LISP...

On Tue, Nov 6, 2018 at 10:35 AM Aaron Ecay <address@hidden> wrote:

Hi Matt,

2018ko azaroak 6an, Matt Price-ek idatzi zuen:
>
> Hi,
>
> I was writing a function to quickly post the ocntents of subtrees to the
> Canvas Learning Management System.  I was trying to strip down the exported
> HTML to an absolute minimum and had forgotten about the body-only paramter
> to org-export-as (!!). So, my solution was to try to rebind
> 'org-html--build-meta-info to always just return "".   However, I can't
> seem to do it properly and I'm wondering if someone can help me figure out
> what's wrong. It's my first time using cl-flet! And I know there are
> various approaches, but I odn't understnad whyt this is notworking, when
> for instance, this does work for me:
>
> (cl-flet ((+
>            (lambda (&rest args) (message "no plus!"))))
>   (+ "whoops"))
> ;; "no plus!"
>
> Meanwhile, here's my  non-functional code:

Quoting from the info page (info "(cl) Function Bindings"):

     The bindings are lexical in scope.  This means that all references
     to the named functions must appear physically within FORMS.

I believe that you can accomplish what you are trying to do with:

(cl-letf (((symbol-function 'org-html--build-meta-info)
           (lambda (&rest args) "")))
  your-code-here)

You could also do something like:

(let ((my-advice (lambda (&rest _) "")))
  (advice-add 'org-html--build-meta-info :override my-advice)
  (unwind-protect
      (progn
        your-code-here)
    (advice-remove 'org-html--build-meta-info my-advice)))

(Why do I think this is better, despite being more verbose?  Advice-add
is specifically designed to change the binding of functions at runtime,
and so it does some specialized things that cl-letf doesnʼt do.  This in
turn means that it should be a more robust way of accomplishing the
desired outcome.)

--
Aaron Ecay