I'm going to withdraw my rant. It's something specific about my stupidity that's causing me these problems. Still investigating.
Ah, I think I see what's been happening. Since I started out with arc I've restricted myself to the mzscheme 'ghetto' and not paid as much attention to the racket language itself. My attitude was "who knows what works in mzscheme and what doesn't." This has been the root cause of my troubles, I think.
Thanks for the link to Guide: Racket. I've also had trouble getting into Racket's documentation, but this looks like a much more accessible starting point than Reference: Racket.