Experiment with the CiteProc-Ruby pre-release!

example.rb

require 'nokogiri' # optional
require 'edtf'     # optional

require 'citeproc'
require 'bibtex'

require 'csl/styles'

cp = CiteProc::Processor.new locale: 'en', style: 'apa', format: 'html'

bib = BibTeX.parse(<<-EOS)
  @article{greenwade93,
    author = "George D. Greenwade",
    title = "The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",
    year = "1993",
    journal = "TUGBoat",
    volume = "14",
    number = "3",
    pages = "342--351"
  }
EOS

bib.convert :latex

cp.import bib.to_citeproc

puts cp.render :citation, id: 'greenwade93', locator: '23'
puts cp.render :citation, id: 'greenwade93', locator: '23-26'

puts cp.render :bibliography, id: 'greenwade93'

# Change the style
cp.options[:style] = 'chicago-author-date'
cp.engine.update!

puts cp.render :bibliography, id: 'greenwade93'

# Parse the CSL Snippet below (can be a full style too)
csl = CSL.parse!(DATA)

# Fetch a citation item from the processor
item = cp['greenwade93']

# Render the item with the csl snippet
puts cp.engine.renderer.render item.cite, csl

__END__
<bibliography>
  <layout suffix=".">
    <group delimiter=" ">
      <label variable="page"/>
      <text variable="page"/>
    </group>
  </layout>
</bibliography>

Gemfile

source 'https://rubygems.org'

gem 'citeproc', :git => 'https://github.com/inukshuk/citeproc.git'
gem 'citeproc-ruby', :git => 'https://github.com/inukshuk/citeproc-ruby.git'
gem 'csl', :git => 'https://github.com/inukshuk/csl-ruby.git'

gem 'nokogiri' # not required: speeds up XML parsing
gem 'edtf'     # not required: more advanced name parsers

gem 'bibtex-ruby'

# not required but convenient: gives you
# local access to all CSL styles and locales
gem 'csl-styles'

Weird, it works now :) Dunno what has changed (I have rebuilt it)