🚀 go-pugleaf

The reason why you have no luck setting the syntax for ^R is that ^R is by
default interpreted by the terminal driver as reprint line.  This can be
changed with stty if you really want ^R.

The fact that (return) must be lexically within the prog isn't the whole
truth.  Were it, then typing (return) at a break-loop wouldn't work either.
The real truth is that the break-loop specifically checks for forms whose
car is return and handles them specially.  (The code is in
/usr/lib/lisp/toplevel.l)  Thus one obvious approach is to extend this
special case code.

A better way is to have the character-macro return a (return) form, not
execute it.  For example:
  (defun return-character-macro (x)
     (if (null x)
         (tconc nil '(return))
	 (tconc x  '||)))	; that's a ctrl-P if you can't see it
  (add-syntax-class 'vfirst-infix-macro '(cinfix-macro escape-when-first))
  (setsyntax '|| 'vfirst-infix-macro 'return-character-macro) ;likewise
together with telling the shell
  stty brk ^P
results in ctrl-P (without needing a return following it) returning from
a break loop.

This assumes you are using the new terminal driver, but nearly anyone does.