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

``````lua

return {

  {

    Meta = get_config

  },

  {

    SmallCaps = SmallCaps,

    Str = Str

  },

  note_filter,

  main_filter

}

``````

where `get_config` just extracts some info from the metadata and populates a table declared at the top of the script which the functions in the other filters refer to.

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)

``````

(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.)

(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!)