How to use pandoc-crossref with Hakyll

Question

I'm trying out Hakyll for an academia-and-math-heavy static website. I'd like to use pandoc-crossref for cross-references to equations.

What is the simplest way to include pandoc-crossref into the compiler chain?

So far, I was able to integrate a bibliography into the compiler like so

pandocComplilerWithBibAndOptions :: Compiler (Item String)
pandocComplilerWithBibAndOptions = do
    csl <- load $ fromFilePath "apa.csl"
    bib <- load $ fromFilePath "bibliography.bib"
    fmap write (getResourceString >>= read csl bib)
    where
        read = readPandocBiblio readerOptions
        write = writePandocWith writerOptions
        readerOptions = defaultHakyllReaderOptions {
            readerExtensions = newExtentions <> pandocExtensions
        }
        writerOptions = defaultHakyllWriterOptions {
            writerExtensions = newExtentions <> pandocExtensions,
            writerHTMLMathMethod = MathJax ""
        }
        newExtentions = extensionsFromList  [Ext_tex_math_double_backslash,
                                             Ext_citations,
                                             Ext_latex_macros]

main :: IO ()
main = hakyll $ do
    ...

    match "posts/*" $ do
        route $ setExtension "html"
        compile $ pandocComplilerWithBibAndOptions
            >>= loadAndApplyTemplate "templates/post.html"    postCtx
            >>= loadAndApplyTemplate "templates/default.html" postCtx
            >>= relativizeUrls

    match "*.bib" $ compile biblioCompiler
    match "*.csl" $ compile cslCompiler

   ...

While this works nicely, I am clueless on how to integrate the cross-references. My best bet would be to express it as some kind of transform and use pandocCompileWithTransformM, but then i wouldn't know how to integrate the bibliography.

Answer 1

Using the Text.Pandoc.CrossRef API

import Text.Pandoc.CrossRef
import Text.Pandoc.Definition (Pandoc) -- pandoc-types

crossRef :: Pandoc -> Pandoc
crossRef = runCrossRef meta Nothing defaultCrossRefAction
  where
    meta = defaultMeta  -- Settings for crossref rendering

Try inserting this between read and write:

    fmap (write . fmap crossRef) (getResourceString >>= read csl bib)

---

Using the pandoc-crossref executable

pandoc-crossref provides a filter as an executable.

The pandoc library has a function applyFilters that lets you run such filters by providing the path to the executable.

applyFilters :: ... -> Pandoc -> m Pandoc

that you can insert between your read and write.

-- 
filterCrossRef :: Pandoc -> PandocIO Pandoc
filterCrossRef = applyFilters env ["pandoc-crossref"] []

There are a few extra steps needed to embed this into the hakyll Compiler monad (probably recompilingUnsafeCompiler in hakyll and something from PandocIO to IO in pandoc).

Answer 2

For better visibility (I found this answer when googling for a similar problem) here is my solution for pandocCompiler users:

For pandocCompiler users here's the code that solved the problem for me:

pandocCompilerWithTransformM defaultHakyllReaderOptions defaultHakyllWriterOptions plantumlFilter
  where
    plantumlFilter = recompilingUnsafeCompiler
      . runIOorExplode
      . applyFilters noEngine def
          [JSONFilter "/usr/local/lib/python3.9/site-packages/pandoc_plantuml_filter.py"]
          []