If you want to indicate they're parameters you're probably best of using syntax that's already being used for parameters like, $a, ?a, :a. I guess {a} is also u

If you want to indicate they're parameters you're probably best of using syntax that's already being used for parameters like, $a, ?a, :a. I guess {a} is also used, but we wanted to avoid braces. Not sure if .a or ~a are good choices. The latter is especially bad since it clashes with common syntax for "(bitwise) not a".