[itishappy]

What, you don't like Arthur's style?

https://www.jsoftware.com/ioj/iojATW.htm

https://github.com/kparc/ksimple/blob/main/ref/a.c

Slightly less factiously, the ksimple repository has a version with comments.

https://github.com/kparc/ksimple

https://github.com/kparc/ksimple/blob/main/a.c

Note, these aren't APL, but they are in the same family of array languages.