x = 0
y = 1
x+y = 0
z = x+y
x+y = 0 (with that specific syntax) will error in pretty much every language.
So we will refuse to allow symbols in identifiers after all?
The only programming languages where arithmetic symbols are allowed identifiers have an identifier sigil (ala Perl, PHP), require whitespace around arithmetic (some teaching languages), or don't have conventional arithmetic syntax (e.g. Forth, Lisp).
If you have something clear you break tokens on, like whitespace (except within quotes), then you should have no problems allowing arbitrary symbols inside an identifier.