A tutorial on programming with folds,combinator-style parsers, and ideas like those expressed in [http://tinyurl.com/8tv2z Functional Programming with Bananas, Lenses, Envelopes and Barbed Wire ] (1991) Erik Meijer, Maarten Fokkinga, Ross Paterson Proceedings 5th ACM Conf.\ on Functional Programming Languages and Computer Architecture, FPCA'91, Cambridge, MA, USA, 26--30 Aug 1991