I wanted a custom prompt for R with ESS. I wanted a double struck R. I probably did it wrong. It never worked. Actually it worked most of the time, and that is worse than never working. Kind people helped me. I still got it wrong. I take full responsibility. It was better not to do it. If you want to try, here is where I left it.
Make the ℝ prompt stand out (be sure to tell ESS how to handle this):
Tell ESS how to handle my custom prompt:
(setq inferior-ess-primary-prompt "ℝ> ")
Handle the custom ℝ prompt in
ess. Don’t use custom here.
(setq inferior-S-prompt "a-zA-Z0-9.*\\(?:[>+.] \\)*ℝ+> ")