Yeah it's one more char, but I think it makes the code more explicit, understandable and also extendable (i.e. '.racket' also becomes an option too - not that it's needed).
>(i.e. '.racket' also becomes an option too - not that it's needed).
.arc / .racket (or .rkt) seems more intuitive than .arc / $
We could also keep the dollar sign in both cases, which I prefer aesthetically, because being familiar with javascript and C type languages, seeing a dot alone like that just seems weird.