@article{Gibbons&Oliveira2008:Essence,
  title = "The Essence of the Iterator Pattern",
  author = "Jeremy Gibbons and Bruno César dos Santos Oliveira",
  year = "2009",
  journal = "Journal of Functional Programming",
  note = "Revised version of \cite{Gibbons&Oliveira2006:Essence}",
  number = "3&4",
  pages = "377-402",
  url = "http://www.comlab.ox.ac.uk/jeremy.gibbons/publications/iterator.pdf",
  volume = "19",
  doi = "10.1017/S0956796809007291",
}