This is just a short article explaining some things I thought about trying to make sense of the term train in Dyalog APL. Some basic knowledge of APL is assumed but not much more than can be attained by browsing an introduction to the language.
There are plenty of rigorous treatments of various aspects of APL out there, but to be clear, this isn’t one. I may get some stuff wrong (please comment below if I do!) but it’s meant to offer an honest view of how one person really goes about thinking in APL.