> [..] Like, in the sense that you can transpile any bit of Python or Lisp or Haskell or Rust or JS into C but the opposite isn’t necessarily true because not all those language support all the features exposed in C [..]

How would you write this (admittedly contrived) Rust function in C without invoking UB:

    pub fn foo(a: &mut i32, b: &mut i32) {
        let (new_a, new_b) = a.checked_mul(*b)
            .map(|new_a| (new_a, b.saturating_sub(*a)))
            .unwrap_or((10, 20));

        *a = new_a;
        *b = new_b;
    }

For those unfamiliar with Rust, it multiplies a by b, and if it didn't overflow:

* a = a * b

* b = b - a, saturating at the minimum value (as in, it won't wrap it just stops there)

If it did overflow:

* a = 10

* b = 20

And finally, does it compiler better: https://godbolt.org/z/66n8W9