I’ve put up a demo of my new Haskell citeproc library here, for those interested:
https://johnmacfarlane.net/citeproc/
This supersedes pandoc-citeproc, which was itself a fork of Andrea Rossato’s citeproc-hs. It is now used in pandoc (with the --citeproc option), but it does not depend on pandoc and can be used outside of it. For those who don’t use Haskell, the library provides a standalone executable that takes in JSON data and spits out JSON results.
The code repository for the library is at https://github.com/jgm/citeproc/ and the API documentation can be found at https://hackage.haskell.org/package/citeproc.