Riddle 4: What’s Going On Here?

What’s happening in this snippet, and why is it interesting?

% q
KDB+ 3.3 2016.03.14 Copyright (C) 1993-2016 Kx Systems
m32/ 2()core 2048MB adavies air.local 10.37.129.2 NONEXPIRE

q)f:{x+1}
q)\d .foo
q.foo)g:{select f a from x}
q.foo)\d .
q).foo.g([]a:1 2 3)
a
-
2
3
4
q)

Riddle 3 Answer

And it looks like I did it again—Riddle 3 has been lacking an official answer for almost a year!
Ciaran Gorman’s answer was correct—strings with leading and/or trailing space are exactly what I was thinking of, and the serialization technique he showed is how to deal with them.
The following function should work as a general solution:

{0x01,($[.z.o like"s*";reverse;::]0x0 vs"i"$10+count x),0x000000f5,("x"$x),0x00}

Hello from Montauk!

I’m at KxCon 2016 in Montauk, and having lots of fun so far. Look me up if you’re here!

github.com/adavies42/qist

q-ist is now on GitHub! I’ve started a new repository, https://github.com/adavies42/qist. My old code from contrib is now available there, but more importantly, I received permission from work to release a collection of utilities and example code from my personal library. This includes a much fuller-featured version of my wtf function, my awq tool for using q as a text filter, dozens of miscellaneous utility functions, and more. I don’t have a README for the whole repository written yet, so to get you started, most of the interesting stuff is in lib, except for awq, which is in bin. Have fun exploring the repository, and feel free to comment or email me with any questions about the code.