Circular lists/shared structures in org-element parse-tree

Circular lists/shared structures in org-element parse-tree

[Thorsten Jolitz]

Hi List, 

I wonder how I can find out in a (elisp) program the points in the parse
tree (returned by org-element-parse-buffer) where shared structures are
used. 

In the read-syntax, its easy to see (especially with `print-circle' set
to non-nil):

#+begin_src emacs-lisp
  #2=(org-data nil #1=(headline (:raw-value "header 1"
   [...] :parent #2#) [...]  
#+end_src

but when processing the parse tree as a list in elisp, how can I detect the
fact that 

,------------
| :parent #2#
`------------

refers to 

,-----------------
| #2=(org-data nil
`-----------------

i.e. points back to an already existing structure?

-- 
cheers,
Thorsten

Re: Circular lists/shared structures in org-element parse-tree

[Daimrod]

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Thorsten Jolitz <tjolitz@gmail.com> writes:

> Hi List, 
>
> I wonder how I can find out in a (elisp) program the points in the parse
> tree (returned by org-element-parse-buffer) where shared structures are
> used. 
>
> In the read-syntax, its easy to see (especially with `print-circle' set
> to non-nil):
>
> #+begin_src emacs-lisp
>   #2=(org-data nil #1=(headline (:raw-value "header 1"
>    [...] :parent #2#) [...]  
> #+end_src
>
> but when processing the parse tree as a list in elisp, how can I detect the
> fact that 
>
> ,------------
> | :parent #2#
> `------------
>
> refers to 
>
> ,-----------------
> | #2=(org-data nil
> `-----------------
>
> i.e. points back to an already existing structure?

AFAIK you have to track all pointers inspected to see if one has already
be seen.

For example, I've implemented a version of equal[1] to compare this kind
of lists (to add tests to org-sync).

[1] https://github.com/daimrod/Emacs-config/blob/master/elisp/dmd-utils.el#L25

-- 
Daimrod/Greg

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Re: Circular lists/shared structures in org-element parse-tree

[Thorsten Jolitz]

Daimrod <daimrod@gmail.com> writes:

> Thorsten Jolitz <tjolitz@gmail.com> writes:

[...]

>> but when processing the parse tree as a list in elisp, how can I
>> detect the fact that
>>
>> ,------------
>> | :parent #2#
>> `------------
>>
>> refers to 
>>
>> ,-----------------
>> | #2=(org-data nil
>> `-----------------
>>
>> i.e. points back to an already existing structure?
>
> AFAIK you have to track all pointers inspected to see if one has already
> be seen.
>
> For example, I've implemented a version of equal[1] to compare this kind
> of lists (to add tests to org-sync).
>
> [1]
> https://github.com/daimrod/Emacs-config/blob/master/elisp/dmd-utils.el#L25

Oh my ... I knew this would complicate my life a bit ...

Thanks for the link, this example function is indeed very helpful. 

-- 
cheers,
Thorsten