Trait frunk_core::hlist::HFoldLeftable

pub trait HFoldLeftable<Folder, Acc> {
    type Output;

    // Required method
    fn foldl(self, folder: Folder, acc: Acc) -> Self::Output;
}

Trait for performing a left fold over an HList

This trait is part of the implementation of the inherent method HCons::foldl. Please see that method for more information.

You only need to import this trait when working with generic HLists or Mappers of unknown type. If the type of everything is known, then list.foldl(f, acc) should “just work” even without the trait.

Required Associated Types

type Output

Required Methods

fn foldl(self, folder: Folder, acc: Acc) -> Self::Output

Perform a left fold over an HList.

Please see the inherent method for more information.

The only difference between that inherent method and this trait method is the location of the type parameters. (here, they are on the trait rather than the method)

Implementors

impl<F, Acc> HFoldLeftable<F, Acc> for HNil

type Output = Acc

impl<F, H, Tail, Acc> HFoldLeftable<F, Acc> for HCons<H, Tail>

where Tail: HFoldLeftable<F, Acc>, F: Fn(Acc, H) -> Acc,

Implementation for folding over an HList using a single function that can handle all cases

use frunk_core::hlist;

let h = hlist![1, 2, 3, 4, 5];

let r: isize = h.foldl(|acc, next| acc + next, 0);
assert_eq!(r, 15);

type Output = <Tail as HFoldLeftable<F, Acc>>::Output

impl<F, R, FTail, H, Tail, Acc> HFoldLeftable<HCons<F, FTail>, Acc> for HCons<H, Tail>

where Tail: HFoldLeftable<FTail, R>, F: FnOnce(Acc, H) -> R,

type Output = <Tail as HFoldLeftable<FTail, R>>::Output

impl<P, R, H, Tail, Acc> HFoldLeftable<Poly<P>, Acc> for HCons<H, Tail>

where Tail: HFoldLeftable<Poly<P>, R>, P: Func<(Acc, H), Output = R>,

type Output = <Tail as HFoldLeftable<Poly<P>, R>>::Output