Interactive prompts already do that. Eg if you google "2+2)*3" it will correctly print "12". This effectively lets you append operations to an expression without editing both sides.
On the other hand, auto closing parentheses in code is a terrible idea for obvious reasons. There are only like 7 languages used in industry and they all have excellent tooling that integrates with your editor to eliminate issues like this.
On the other hand, auto closing parentheses in code is a terrible idea for obvious reasons. There are only like 7 languages used in industry and they all have excellent tooling that integrates with your editor to eliminate issues like this.