Macro rec_fold 

macro_rules! rec_fold {
    ($in_list:expr, $accum:expr, $($func:tt)*) => { ... };
}

Helper for writing const fn equivalents of NList::fold

This macro acts like a function with this signature:

use nlist::{NList, PeanoInt};

use nlist::receiver::Receiver;

fn rec_fold<'a, P, T, L, F, U>(list: P , accum: U, func: F) -> U
where
    P: Receiver<'a, NList<T, L>>,
    L: PeanoInt,
    T: 'a,
    F: FnOnce(
        ... // parameter types explained below
    ) -> U

The closure is only called when the list is non-empty (i.e.: when L != 0).

The closure parameters depend on the value of P:

• If P == NList<T, L>: the parameters are (T, Nlist<T, L::SubOneSat>)
• If P == &NList<T, L>: the parameters are (&T, &Nlist<T, L::SubOneSat>)
• If P == &mut NList<T, L>: the parameters are (&mut T, &mut Nlist<T, L::SubOneSat>)

Accumulator Argument

The accum argument is only evaluated if the list is empty, which means that you can pass it by value and still use it in the passed in closure.

Example

By value

Example that takes an NList by value

use nlist::{NList, Peano, PeanoInt, nlist};
 
const SUM: u128 = add_up(0, nlist![1, 2, 3, 4, 5]);
 
assert_eq!(SUM, 15);
 
const fn add_up<L>(sum: u128, list: NList<u128, L>) -> u128
where
    L: PeanoInt
{
    nlist::rec_fold!{list, sum, |elem: u128, next| add_up(sum + elem, next)}
}

By reference

Example that takes an NList by reference

use nlist::{NList, Peano, PeanoInt, nlist};
 
const SUM: u128 = add_up(0, &nlist![3, 5, 8]);
 
assert_eq!(SUM, 16);
 
const fn add_up<L>(sum: u128, list: &NList<u128, L>) -> u128
where
    L: PeanoInt
{
    nlist::rec_fold!{list, sum, |elem: &u128, next| add_up(sum + *elem, next)}
}