I don't know a bit of APL, but I see numbers 3 and 4 and suspiciously looking pair of triples of -1, 0 and 1. Thus, this program of yours has game of life step

I don't know a bit of APL, but I see numbers 3 and 4 and suspiciously looking pair of triples of -1, 0 and 1. Thus, this program of yours has game of life step function somewhere there. The "writeonlyness" is in the eyes of beholder, and I am almost not joking - we see better what we expect to see. It is possible to determine algorithms by their structure which rarely changes much betweend different languages. But, I have 34 years of experience in software development and I often delve into very strange languages out of curiosity and to find what does unify them or make them special for some particular tasks.