Trait Foldable

Source

pub trait Foldable<F: HKT> {
    // Required method
    fn fold<A, B, Func>(fa: F::Type<A>, init: B, f: Func) -> B
       where Func: FnMut(B, A) -> B;
}

Expand description

Re-exports the Foldable trait for reducing data structures. The Foldable trait abstracts over data structures that can be reduced to a single summary value.

It provides a fold operation (also known as reduce or inject) that applies a binary function to an accumulator and each element of the structure, from left to right.

This trait is generic over F, which is a Higher-Kinded Type (HKT) witness.

§Laws (Informal)

Fold right equivalence: foldr f z t = foldl (flip f) z (reverse t) (if reverse is defined)
Fold identity: fold f z (pure x) = f z x (if pure is defined)

§Type Parameters

F: A Higher-Kinded Type (HKT) witness that represents the type constructor (e.g., OptionWitness, ResultWitness<E>, VecWitness).

Required Methods§

Source

fn fold<A, B, Func>(fa: F::Type<A>, init: B, f: Func) -> B
where Func: FnMut(B, A) -> B,

Reduces the elements of the structure to a single value by applying a function.

This is equivalent to a left-fold (foldl) operation. It traverses the structure, applying the f function to an accumulating value and each element.

§Arguments

fa: The data structure (F::Type<A>) to fold.
init: The initial value of the accumulator.
f: A binary function that takes the current accumulator and an element from the structure, and returns the new accumulator value.

§Returns

The final accumulated value after processing all elements.

§Type Parameters

A: The type of the elements within the foldable structure.
B: The type of the accumulator and the final result.
Func: The type of the folding function, which must be FnMut(B, A) -> B.

§Examples

use deep_causality_haft::{Foldable, OptionWitness};

let opt = Some(5);
let sum = OptionWitness::fold(opt, 0, |acc, x| acc + x);
assert_eq!(sum, 5);

let none_opt: Option<i32> = None;
let sum_none = OptionWitness::fold(none_opt, 0, |acc, x| acc + x);
assert_eq!(sum_none, 0);