odomanov/citeproc

CSL citation processing library in Haskell

citeproc

This library generates citations and bibliography formatted according to a CSL style. Currently version 1.0.2 of the CSL spec is targeted.

This library is a successor to pandoc-citeproc, which was a fork of Andrea Rossato's citeproc-hs. I always found it difficult to fix bugs in pandoc-citeproc and decided that implementing citeproc from scratch would give me a better basis for understanding. This library has a number of other advantages over pandoc-citeproc:

• it is much faster (as a rough benchmark, running the CSL test suite takes less than 4 seconds with this library, compared to 12 seconds with pandoc-citeproc)

• it interprets CSL more faithfully, passing more of the CSL tests

• it has fewer dependencies (in particular, it does not depend on pandoc)

• it is more flexible, not being tied to pandoc's types.

Unlike pandoc-citeproc, this library does not provide an executable. It will be used in pandoc itself to provide integrated citation support and bibliography format conversion (so the pandoc-citeproc filter will no longer be necessary).

How to use it

The main point of entry is the function citeproc from the module Citeproc. This takes as arguments:

• a CiteprocOptions structure, which includes the following options:

  • linkCitations controls whether citations are hyperlinked to the bibliography.

  • linkBibliography automatically linkifies any identifiers (DOI, PMCID, PMID, or URL) appearing in a bibliography entry. When an entry has a DOI, PMCID, PMID, or URL available but none of these are rendered by the style, add a link to the title (or, if no title is present, the whole entry), using the URL for the DOI, PMCID, PMID, or URL (in that order of priority). See Appendix VI of the CSL v1.0.2 spec.

• a Style, which you will want to produce by parsing a CSL style file using parseStyle from Citeproc.Style.

• Optionally a Lang, which allows you to override a default locale,

• a list of References, which you can produce from a CSL JSON bibliography using aeson's decode,

• a list of Citations (each of which may have multiple CitationItems).

It yields a Result, which includes a list of formatted citations and a formatted bibliography, as well any warnings produced in evaluating the style.

The types are parameterized on a CiteprocOutput instance a, which represents formatted content in your bibliographic fields (e.g. the title). If you want a classic CSL processor, you can use CslJson Text. But you can also use another type, such as a pandoc Inlines. All you need to do is define an instance of CiteprocOutput for your type.

The signature of parseStyle may not be self-evident: the first argument is a function that takes a URL and retrieves the text from that URL. This is used to fetch the "indendent parent" of a dependent style. You can supply whatever function you like: it can search your local file system or fetch the content via HTTP. If you're not using dependent styles, you can get by with \_ -> return mempty.

The citeproc executable

If the package is compiled with the executable flag, an executable citeproc will be built. citeproc reads a JSON-encoded Inputs object from stdin (or from a file if a filename is provided) and writes a JSON-encoded Result object to stdout. This executable can be used to add citation processing to non-Haskell projects.

citeproc --help will summarize usage information. See the man page for more information.

Known bugs and limitations

Although this library is much more accurate in implementing the CSL spec than pandoc-citeproc was, it still fails some of the tests from the CSL test suite (62/818). However, most of the failures are on minor corner cases, and in many cases the expected behavior goes beyond what is required by the CSL spec. (For example, we intentionally refrain from capitalizing terms in initial position in note styles. It makes more sense for the calling program, e.g. pandoc, to do the capitalization when it puts the citations in notes, since some citations in note styles may already be in notes and in this case their rendering may not require capitalization. It is easy to capitalize reliably, hard to uncapitalize reliably.)