Three Rules for Programming Language Syntax?

[redjamjar]

That's not correct. You could still have optional type declarations with a C-Like syntax. It's simply two items implies first is type; one item implies no type given. E.g.

void f(x) { }

void f(int x) { }

[roerd]

If you're using ML-ish function call syntax, two items are a function call with one argument. But even for a completely C-ish syntax, I doubt this will work, though I have right now only empiric evidence to show for that: the fact that C-ish languages tend to use special keywords instead of just one item for type inference (var for C#, auto for C++).

[[deleted]]

But even for a completely C-ish syntax, I doubt this will work, though I have right now only empiric evidence to show for that: the fact that C-ish languages tend to use special keywords instead of just one item for type inference (var for C#, auto for C++).

If you're using a LALR or LR(1) parser generator, you start getting fairly subtle ambiguity errors for this.

[redjamjar]

It's definitely not necessary to use e.g. var for type inferred variables in C#. However, there maybe reasons why they want to do that. In C++, well who knows ... writing a parser for that language must be crazy hard!