It looks like something went wrong with the current snapshot for BC on the Utah server. This returns a 404: https://www.cs.utah.edu/plt/snapshots/current/installers/racket-current-x86_64-macosx-bc.dmg

About separating digits in ~r: #\, instead of "," is easier to handle internally and faster (cons instead of append). Is there an incentive to allow for strings for the separator?

This is fallout from the build-system change — particularly that it failed enough times for the link to go away. I’m not sure exactly what went wrong on the most recent try, but I’ll keep working to get it through.