AW: slide: useful function?

[Tom Pledger]

Nick Name writes:
 :
 | Ok I can't resist longer. It's ages I have been wondering what's a
 | catamorphism, and an anamorphism, and what the hell does it mean
 | "data is expressed by destructors and not by constructors", but I
 | have had no time till now. Please some of you all catamorphism
 | experts tell me a good and clear article to read :)))

As a reader but not an expert, I recommend
http://www.cse.ogi.edu/~mpj/pubs/springschool.html