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Re: How to add new type of block to a derived back-end?

From: Salomon Turgman
Subject: Re: How to add new type of block to a derived back-end?
Date: Sat, 11 Apr 2020 21:58:00 -0400

Ok... just reporting back my progress in case it helps someone else. Bur first, all the stuff that you can do with src blocks is stuff I never imagined. Seems like the possibilities are endless. Here is what I did so far:

#+NAME: simulation
#+HEADER: :var cap="DEFAULTCAPTION" :cache yes :eval no-export :var altimage="1_image.svg#img1"
#+BEGIN_SRC emacs-lisp :var divid="defid" :var num=1 :results html :exports results
"<div class=\"caption\">Simulation %s: %s</div>
  <div class=\"simulation\">
    <div id=\"%s\">
          <use xlink:href="" </use>
  <script>var app = Elm.%s.init({node: document.getElementById(\"%s\")});</script>"
num cap divid altimage (capitalize divid) divid)

That is my "definition"... I call it like this:

#+CALL: simulation(cap="Manual control of tank level", num=1, divid="main1", altimage="1_manual_noscript.svg")

And it seems to work beautifully. Still need to figure out the counting of the number of simulations per page... but that should be trivial at this point. Thank you so much for all the pointers.


On Fri, Apr 10, 2020 at 1:14 PM Salomon Turgman <address@hidden> wrote:
Thank you very much. I will explore what you suggest. I'm glad I emailed, seems like I was going down the wrong path.


On Fri, Apr 10, 2020, 1:10 PM Berry, Charles <address@hidden> wrote:
Salomon, see inline comments below.



> On Apr 10, 2020, at 7:56 AM, Salomon Turgman <address@hidden> wrote:
> Hello all,
> Thanks in advance for any hints you can provide for this. I am trying to create a derived back-end that handles a new type of block in org-mode. I am trying to derive using the html export backend as a parent.
> Currently I am solving my problem like this:
> #+CAPTION[Manual control]: Simulation 1: Manual control of the tank level.
> <div class="caption">Simulation 1: Manual control of the tank level.</div>
> <div class="simulation">
> <div id="main1">
> <noscript>
> Some other cool stuff here.
> </noscript>
> </div>
> </div>
> <script>var app = Main1.init({node: document.getElementById("main1")});</script>
> This has a few downsides:
> 1. I have to specify the caption twice since export translator does not handle captions.
> 2. I have to include substantial amounts of html.
> 3. I have keep track of references to simulations manually (simulation 1, simulation 2, etc)
> 4. I have to include the identifier `main1` or `Main1` in several locations in the snippet.
> I could solve some of this with an automated snippet insertion tool but I thought that maybe I can get the export back-end to do most of the work for me.
> So I am trying to derive as follows (in pseudo-elisp-code):
> (require 'ox)
> (require 'ox-html)
> (org-export-define-derived-backend 'textbook 'html
>   :menu-entry
>   '(?I "Export textbook section"
>        ((?b "To buffer" org-html-export-as-html)
>               (?I "To file" org-html-export-to-html)
>               (?o "As HTML file and open"
>             (lambda (a s v b)
>               (if a (org-html-export-to-html t s v b)
>                       (org-open-file (org-html-export-to-html nil s v b)))))))
>   :translate-alist '((simulation . org-textbook-simulation)))

>From the `org-export-define-backend' docstring:

"TRANSCODERS is an alist between object or element types and
functions handling them."

But `simulation' is not such a type. So, this will not work.

> (defun org-textbook-simulation (element contents info)
>   (let* ((simnum (extract simnum value))
>               (caption (org-export-get-caption element))
>          (divid (extrac divid value))
>               (modid (convert divid into modid))
>          )
>     (format "<div class=\"caption\">Simulation %simnum%: %Caption%.</div>
>   <div class=\"simulation\">
>     <div id=\"%divid%\">
>     </div>
>   </div>
> <script>var app = %modid%.init({node: document.getElementById(\"%divid%\")});</script>"
>    simnum caption divid modid divid)))
> With the hope that I can do something like this in my .org file:
> #+CAPTION[Manual control]: Simulation 1: Manual control of the tank level.
> Some other cool stuff here

I think an easier approach is to write a babel src-block that formats the inputs you need and creates a value that is your desired output.

Use `:var' header arguments to define the inputs.

Use `:wrap html' to prevent the exporter from changing the output.

Subsequent calls can use the `#+CALL' idiom.

You can use any scripting language that suits you - elisp, python, shell, R, ... --- for this purpose.

If you are skilled in emacs-lisp you might write an `eval' macro instead of a src block.

> Am I on the right track here? Can someone point me to an example on how to:
> 1. Keep track of the number of simulations for referencing?

Using the babel approach, you would need a `:session' with a persistent variable that would hold the count. You would need to initialize it in your document so that subsequent exports will start counting at zero.

> 2. Extract the caption properly? The above is just my guess.

IIRC, the info channel is not populated when babel runs, so you will need to parse the src-block and extract the `:caption' element. I think you can use a `:var cap=(find-caption)' idiom, where `find-caption' is a function you write using `org-element-context' as a starting point.

Or if the only need you have for the caption is within that src block just use `:var cap="<your caption here>".

> 3. Extract the divid value (main1)

:var divid="main1"

> 4. And finally, how to get org to recognize the new SIMULATION block so that it can apply `org-textbook-simulation`? Do I need to register this type of block somewhere? Or is the name of the first member of the :translate-alist translation pair have some special meaning?

Don't go in that direction. Use babel or write an eval macro.


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