I've been told that the guy who wrote this believe that the brain only has a limited buffer to compute source code. So he is trying to use the shortest code possible everywhere.
I think looking at this code has already caused a buffer overrun in my brain ;)
"This is being used everyday in production by most financial institutions" — you can't be serious...
I'm not surprised, it's an APL family language.
KDB developers make BIG money. It's an APL-like language and used to analyze financial time-series.
It looks more like the guy that wrote this wanted good job security and pay, and ended up making and industry with good job security and pay.