"In this article we'll get a brief introduction to the J programming language.
The goal is to wet your appetite for an exciting programming paradigm
rather than providing an in-depth introduction. As we move along we'll
learn just enough J to explore a fascinating corner of the language that
lets us manipulate functions as data. You'll see how these techniques
differ from traditional functional programming, why manipulating
functions is interesting and how it lets you solve real problems with a
minimum of code."
http://www.adamtornhill.com/articles/jlang/beyondfunctional.html