We have a good number of macros that might benefit from this in XEmacs, most of them here. (https://bitbucket.org/xemacs/xemacs/src/0df3cedee9ac/src/lisp.h#cl-1984) (Not the sort of code your average C programmer is that comfortable with, I admit.) Other things are more of a priority at the moment, but I'll bookmark your paper. Thanks!

Yes, I see what you mean! Though it looks to me as if most of those loops fit reasonably well into a for statement, with the only annoying part being the need to declare some variables up front. I don't know what XEmacs's portability requirements are, but if they include C89 then you might find that my trickery doesn't benefit you after all due to the one extra-C89 feature (bringing declarations into scope via for initialisers) not being available to you.