The J Incunabulum (Remembering Ken Iverson, 2004)

Here is also a very interesting discussion on Sayeret Lambda. Shai Berger's (quoting his brother) are very good reading:

https://groups.google.com/forum/?fromgroups#!topic/sayeret-l...

E.g., the J parsing code written in a similar idiomatic way is some of the most simple and beautiful I've seen:

https://github.com/openj/core/blob/master/p.c