Macro function 

macro_rules! function {
    ($( $(+)? $c0:literal $(x $( ^ $d0:literal )?)? )+) => { ... };
    ($name:ident (x) = $($rest:tt)+ ) => { ... };
    (const $name:ident (x) = $($rest:tt)+ ) => { ... };
    (static $name:ident (x) = $($rest:tt)+ ) => { ... };
}

Macro to generate a monomial polynomial function.

This is good for using as a data source for testing

• Terms can be listed in any order
• Same-power terms are summed
• Missing terms are 0

The only major limitation is that it needs a space between the coefficient and the variable:

• 20.0 x^3 is valid, but 20.0x^3 is not.

Syntax:

function!(
    [const | static]?
    [<name>(<x>) = ]?
    [ [+]? <coef> [ x [ ^ <deg> ]? ]? ]+
)

Example

function!(test(x) = 20.0 x^3 + 3.0 x^2 - 2.0 x + 4.0); // Normal let-binding
function!(const test2(x) = 20.0 x^3 + 3.0 x^2 - 2.0 x + 4.0); // const! can live outside functions
function!(static test3(x) = 20.0 x^3 + 3.0 x^2 - 2.0 x + 4.0); // I added static for some reason
let test4 = function!(20.0 x^3 + 3.0 x^2 - 2.0); // No auto bindings

// Evaluate at x = 5
println!("{}", test.y(5.0));

// You could visualize it too:
// polyfit::plot_function!(test, x_range = 0.0..1000.0);