Re: Converting filter to custom writer

[Albert Krewinkel <albert+pandoc-9EawChwDxG8hFhg+JK9F0w@public.gmane.org>]

BPJ <melroch-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:

> I saw no answer to this one.

Thanks for the reminder :)

> Den fre 24 juni 2022 16:09BPJ <> skrev:
>
> I have a not-so-old "pseudo-writer" implemented as a filter which
> mostly injects  tons of raw markup into the document tree so that the
> output of the plain writer looks like my target format, returning a
> table of filters at the end like this
>
> [...]
>
> Am I right that I in principle could convert this into a new style
> custom writer by removing the Meta filter, replacing `return
> {<filters>}` above with `local filters = {<filters>}` and adding the
> following at the bottom of the script?
>
> ``````lua
> function Writer (doc, opts)
>   get_config(doc.meta)
>   for _,filter in ipairs(filters) do
>     doc = doc:walk(filter)
>   end
>   doc.blocks = blocks
>   return pandoc.write(doc, 'plain', opts)
> ``````

Yes, I believe that would work. I'm actually starting to use custom
writers in a similar way. The only downside is that you can't use the
default extension mechanism (like `plain-multiline_tables`) on the
command line to tune the writer, but we're working on that.

> (This got me thinking: what if `walk` accepted one more argument which
> will be passed as an extra argument to the functions in the filters,
> which could be used to pass config and/or maintain state? It somehow
> feels more intuitive than defining a table outside the metadata handler
> which all handlers close around.)

Good idea. Although I have to admit that I'm not really enthusiastic
about it due to many small, slightly annoying changes that implementing
this feature would require in the Haskell code.

> (BTW the main reason that the `note_filter` is separate is that it
> needs to be topdown because it counts and collects the notes, while
> `main_filter` needs to be bottomup because it sometimes relies on the
> content of elements already having been processed. I was very happy
> when I realized that this would work!)

😊

-- 
Albert Krewinkel
GPG: 8eed e3e2 e8c5 6f18 81fe  e836 388d c0b2 1f63 1124

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