I’m trying to recover, before trying to rewrite, a “classic” pandoc custom writer called tba.lua.

Thus far, I’ve managed to make it work by adding the prescribed patch in the form

function Writer (doc, opts)
  PANDOC_DOCUMENT = doc
  PANDOC_WRITER_OPTIONS = opts
  loadfile(PANDOC_SCRIPT_FILE)()
  return pandoc.write_classic(doc, opts)
end

as stated in the documentation.

But then, I need to add always a --template option to load the template, as the writer in standalone mode complains about

No template defined in tba.lua

While seeing another example in the documentation, I tried to define the template in the writer by adding

function Template ()
 local template = pandoc.template
 return template.compile(template.default 'tba.lua')
end

Pandoc now can find the template default.tba.lua in the --data-dir directory, but now complains that

Error running Lua:
string expected, got pandoc Template

I thought that template.compile would return the string, so I don’t know what went wrong.