lens-rs

lens implemented in rust

the Review optics describes how to construct a single value.
A Traversal can access the multiple substructures.
A Prism can access the substructure may exist.
A Lens can access the substructure must exist.

Example

access the substructure

fn test() -> Option<()> {
    let mut nested: Result<Result<_, ()>, ()> = optics!(Ok.Ok).review((1, 2));
    *optics!(Ok.Ok._0).pm_mut(&mut nested)? += 1;
    assert_eq!(optics!(Ok.Ok._0).pm(nested)?, 2);

    let mut x = (1, (2, (3, 4)));
    *optics!(_1._1._1).view_mut(&mut x) *= 2;
    assert_eq!(optics!(_1._1._1).view(x), 8);

    let mut x: (_, Result<_, ()>) = (1, Ok((2, 3)));
    *optics!(_1.Ok._1).pm_mut(&mut x)? *= 2;
    assert_eq!(optics!(_1.Ok._1).pm(x)?, 6);

    let mut x = (1, vec![Some((2, 3)), None]);
    optics!(_1._mapped.Some._0)
        .traverse_mut(&mut x)
        .into_iter()
        .for_each(|i| *i += 1);
    assert_eq!(optics!(_1._mapped.Some._0).traverse(x), vec![3]);

    Some(())
}

derive lens for data types

use lens_rs::*;

#[derive(Review, Prism, Debug)]
enum AnEnum<T> {
    A(T, i32),
    #[optic] B(T),
}

#[derive(Lens, Debug)]
struct Foo {
    #[optic] a: i32,
    #[optic] b: i32,
}


fn test() -> Option<()> {
    let x = optics!(Some.B).review(Foo {
        a: 3,
        b: 2,
    });
    assert_eq!(optics!(Some.B.b).pm(x)?, 2);
    
    Some(())
}

assume a type T may have substructure that the type is i32.

fn bar<T, Pm: Prism<T, To=i32>>(t: &mut T, pm: Pm) {
    pm.pm_mut(t).map(|x| *x += 2);
}

fn test() {
    let mut complex = (1, Ok((Err(2), 3)));
    bar(&mut complex, optics!(_0));
    bar(&mut complex, optics!(_1.Err)); // do nothing
    bar(&mut complex, optics!(_1.Ok._0.Ok)); // do nothing
    bar(&mut complex, optics!(_1.Ok._0.Err));
    bar(&mut complex, optics!(_1.Ok._1));
    assert_eq!(complex, (3, Ok((Err(4), 5))));
}

assume a type T must have a field .a.

fn with_field_a<T>(t: T) -> String
where
    field![a]: Lens<T, To=String>
{
    optics!(a).view(t)
}

let foo = Foo {
    a: "this is Foo".to_string(),
    b: ()
};
let bar = Bar {
    a: "this is Bar".to_string(),
    c: 0
};

println!("{}", with_field_a(foo));
println!("{}", with_field_a(bar));

Cargo.toml

add it in Cargo.toml

[package.metadata.inwelling]
lens-rs = true

lens-rs 0.1.3

lens-rs

Example

Cargo.toml