What can and can I not put into an expression

It depends on whether Julia can parse it, and indeed the way to find out is to try to make an expression. There are a bunch of unicode operatores, which probably include all sorts of arrows, maybe that could be for you?

Edit: haha, you beat me to it… ~~Also please quote your code, see https://discourse.julialang.org/t/psa-how-to-quote-code-with-backticks/7530~~