Macro for writing expressions

[lightclient]

The most simplified form of a complex expression currently looks like this:

//((1+2)*3-(4/2) = 7
let expr = Expression::Minus(
    Expression::Times(
        Expression::Plus(
            Terminal::Number(1.into()).into(),
            Terminal::Number(2.into()).into(),
        ).into(),
        Terminal::Number(3.into()).into(),
    ).into(),
    Expression::Divide(
        Terminal::Number(4.into()).into(),
        Terminal::Number(2.into()).into(),
    ).into(),
);

It would be great to write a macro so you can write it like this:

//((1+2)*3-(4/2) = 7
let expr = expr! {
    Minus(
        Times(
            Plus(Number(1), Number(2)),
            Number(3)
        ),
        Divide(Number(4), Number(2))
    )
};

[lightclient]

Sam recommended just overriding the math operators for the Expression type, and as usual, his approach is much simpler. So we can do that instead.