Macro co 

macro_rules! co {
    ($re:expr, $im:expr) => { ... };
    ($re:expr) => { ... };
}

Macro for creating complex numbers with real and imaginary parts

Examples

let c1 = co!(1.0, 2.0);    // 1 + 2i
let c2 = co!(3.0);         // 3 + 0i (real number)