Call site analysis and such are ways to do that. That's for example the difference between TypeScript and Flow. The later does stuff like that (which is both a

Call site analysis and such are ways to do that. That's for example the difference between TypeScript and Flow. The later does stuff like that (which is both a boon and a bane. Its amazingly powerful, but you can get into states where figuring out why you're getting a compile time error is a mind fuck. Languages Elm handle it beautifully though.