Monadic blockRender?

[mrkgnao]

I'd like to render LaTeX diagrams into images that are then inserted into the output. I have a function of the following form:

-- | Render some LaTeX content to an image whose filename is the 
-- hash of the content. Return the path to the image.
renderToFile :: Text -> IO FilePath
renderToFile latex = do
   ...
   pure savePath

I think the interface I would like is to interpret code-blocks with some particular infostring (e.g. render-latex) as LaTeX to be rendered into a PNG. If blockRenderM existed, I could just do

renderLatexExt :: Extension
renderLatexExt = blockRenderM $ \case
  CodeBlock (Just "render-latex") content 
    -> (\uri -> Image undefined uri Nothing) <$> renderToFile content
  x -> pure x

or something.

[mrkkrp]

I have exposed enough of the internal machinery in #116, so it should be possible to write arbitrary custom renders.

[emekoi]

I actually implemented #116 in a local fork of mmark to try to write a monadic renderer and I don't think it's sufficient since extensions and renderers are currently pure (they are basically records of Endos) and specialized to produce HtmlT Identity () so you can't change the underlying monad. Supporting monadic extensions and renderers amounts to replacing Endo a with Kleisli m a a so you get some type like MMarkT m and MMark = MMarkT Identity.

[mrkkrp]

@emekoi Could you open a PR for that?