Shared via Rust Playground

playground.rs

#![feature(optin_builtin_traits)]
use std::marker::PhantomData;

struct Nil;
struct Cons<H, T>(H, T);

struct Zero;
struct One;

trait UInt {
    fn value() -> u64;
}

impl UInt for Nil {
    fn value() -> u64 { 0 }
}

trait Bits: UInt {}

impl Bits for Nil {}

impl<T: Bits> Bits for Cons<Zero, T> {}
impl<T: Bits> Bits for Cons<One, T> {}

impl<T: Bits> UInt for Cons<Zero, T> {
    fn value() -> u64 { T::value() << 1 }
}

impl<T: Bits> UInt for Cons<One, T> {
    fn value() -> u64 { (T::value() << 1) | 1 }
}

trait Add_<A, B> { type Out; }
type Add<A, B> = <() as Add_<A, B>>::Out;

impl Add_<Nil, Nil> for () { type Out = Nil; }

impl<H, T> Add_<Cons<H, T>, Nil> for () { type Out = Cons<H, T>; }
impl<H, T> Add_<Nil, Cons<H, T>> for () { type Out = Cons<H, T>; }

impl<T1: Bits, T2: Bits> Add_<Cons<Zero, T1>, Cons<Zero, T2>> for ()
where (): Add_<T1, T2>
{ 
    type Out = Cons<Zero, Add<T1, T2>>; 
}

impl<T1: Bits, T2: Bits> Add_<Cons<Zero, T1>, Cons<One, T2>> for ()
where (): Add_<T1, T2>
{ 
    type Out = Cons<One, Add<T1, T2>>; 
}

impl<T1: Bits, T2: Bits> Add_<Cons<One, T1>, Cons<Zero, T2>> for ()
where (): Add_<T1, T2>
{ 
    type Out = Cons<One, Add<T1, T2>>; 
}

impl<T1: Bits, T2: Bits> Add_<Cons<One, T1>, Cons<One, T2>> for ()
where (): Add_<T1, T2> + Add_<Cons<One, Nil>, Add<T1, T2>>
{ 
    type Out = Cons<Zero, Add<Cons<One, Nil>, Add<T1, T2>>>; 
}

trait Mul_<A, B> { type Out; }
type Mul<A, B> = <() as Mul_<A, B>>::Out;

fn main() {
    // LSB ---> MSB
    type Five = Cons<One, Cons<Zero, Cons<One, Nil>>>;
    type Three = Cons<One, Cons<One, Nil>>;
    type Eight = Add<Five, Three>;
    println!("{}", <Eight as UInt>::value());
    //println!("{}", Add::<Five, Three>::value());
}