bad optics

ergonomic lenses in rust

bad-optics implements the haskell concept of lenses, prisms, and traversals in rust

it does not implement the operators, as it's not really a thing we can do in rust

you will need nightly for this library to work, as it uses a bunch of unstable features. they're technically not critical, but i think not having them reduces the ergonomics too much

does bringing lenses into rust actually make sense? probably not, but it was fun to implement so who can say

example

use bad_optics::{
    lenses::{over, set},
    prelude::*,
};

fn main() {
    let a = ((1, 2), 3);

    // use view to access inside the tuple
    let res = view(_0, a);
    assert_eq!(res, (1, 2));

    let res = view(_1, a);
    assert_eq!(res, 3);

    // you can combine lenses
    let lens = _0 + _1;

    // use the view function to access
    let res = view(lens, a);
    assert_eq!(res, 2);

    // you can also call the lens as a function
    let res = lens(a);
    assert_eq!(res, 2);

    // call the over function to modify the value
    let a = over(lens, a, |v| v + 1);
    assert_eq!(a, ((1, 3), 3));

    // call the set function to set the value
    let a = set(lens, a, 5);
    assert_eq!(a, ((1, 5), 3));

    // you can also call the lens as a function to modify the value
    let res = lens(a, |v| v + 1);
    assert_eq!(res, ((1, 6), 3));
}

how to use

bad-optics provides some of the lenses, prisms, and traversals defined in lens. i'm still trying to add more, so if there's one you need and it's missing from here, feel free to open a PR

if you don't know how lenses work, this is not really gonna be a tutorial, you should read this first instead. the general idea is that they are first-class getters and setters