Posted on November 9, 2014

Displaying bibTeX in Hakyll

My personal site has been powered by Hakyll for a while. I like being able to rsync static html to my Raspberry Pi server. It gives me fewer security issues to worry about. Being an academic, one of the reasons I have a website is to list my publications for the world. Not that the world is too interested, but it helps when someone Google’s your name. Since I started using Hakyll I’ve had to duplicate my publications data, once for use with LaTeX (the least worse system for producing a print document) and once as my publications.html on this site. The computer scientist in my hates this as it violates the Don’t Repeat Yourself principle. So, how can I get Hakyll to generate my publications.html from my BibTeX data? Read on for a solution.

The core idea here is to generate IO [Item String] so that I can use Hakyll’s unsafeCompiler to generate a Compiler [Item String] which can then list each of the items as a bibliographic entry. It’d be a bit smarter to generate [Item Bibentry] where Bibentry is some complex bibliography record, but for the moment this suffices. In this simple solution I use Parsec to parse the BibTeX file:

getCitations :: String -> IO [Text.BibTeX.Entry.T]
getCitations fname =
  Parsec.parseFromFile (Parsec.skipMany >> Parse.file) fname >>= either reportError return
    reportError = error "Moo"

Yeah, error handling leaves a lot to be desired.

Given the IO [Entry.T] we need to turn them into HTML strings. For this we’ll employ the awesome Pandoc to change any LaTeX formatted strings into HTML structure.

paraToPlain :: Block -> Block
paraToPlain (Para x) = Plain x

htmlize :: String -> String
htmlize latex = writeHtmlString def p
    p = topDown paraToPlain (readLaTeX def latex)

The only complexity here is that, by default, Pandoc will generate the string \textbf{foo} as <p><strong>foo</strong></p> whereas I’d prefer <strong>foo</strong>. Hence I have to do the topDown walking of the Pandoc document structure converting any Para into a Plain. After that, it’s a case of pulling out each bibliographic entry and htmlizing it:

getField :: Entry.T -> String -> String
getField entry field = htmlize (fromJust (lookup field (Entry.fields (Entry.lowerCaseFieldNames entry))))

getFields :: Entry.T -> [String] -> [String]
getFields entry xs = map (getField entry) xs

getConf :: Entry.T -> Item String
getConf entry = Item {itemIdentifier = id,
                          itemBody = body}
    id = fromFilePath (Entry.identifier entry)
    body = intercalate ", " (getFields entry ["author", "title", "booktitle", "pages", "year"])

cite :: Entry.T -> Item String
cite entry =
  case (Entry.entryType entry) of
    "article" -> getArticle entry
    "proceedings" -> getProceedings entry
    "inproceedings" -> getConf entry

As we now have something suitable for unsafeCompiler we can then use Hakyll to generate a HTML file as we normally would, where the content of templates/publications.html is a simple <ul>.

create ["publications.html"] $ do
  route idRoute
  compile $ do
    books <- getCiteCompiler "/home/aidan/SparkleShare/Proposals/books.bib"
    journals <- getCiteCompiler "/home/aidan/SparkleShare/Proposals/journals.bib"
    confs <- getCiteCompiler "/home/aidan/SparkleShare/Proposals/conferences.bib"
    let pubCtx =
          listField "books" defaultContext (return books) `mappend`
          listField "journals" defaultContext (return journals) `mappend`
          listField "confs" defaultContext (return confs) `mappend`
    makeItem ""
      >>= loadAndApplyTemplate "templates/publications.html" pubCtx
      >>= loadAndApplyTemplate "templates/default.html" pubCtx
      >>= relativizeUrls

A full solution fills in the blanks of the above description. As my Blog (and the rest of my life) is stored in git, I’ve made it available on github.