Shared via Rust Playground

playground.rs

trait ShortCircuit {
    fn short(&self) -> 
}

trait And<Rhs=Self> {
	type Output;
	fn short(&self) -> Option<Self::Output>;
	fn and(self, rhs: Rhs) -> Self::Output;
}

trait Or<Rhs=Self> {
    type Output;
    fn short(&self) -> Option<Self::Output>;
    fn or(self, rhs: Rhs) -> Self::Output;
}

macro_rules! and {
	($a:expr, $b:expr) => {{
		let a = $a;
		match And::short(&a) {
			Some(v) => v,
			None => And::and(a, $b),
		}
	}}
}

macro_rules! or {
    ($a:expr, $b:expr) => {{
        let a = $a;
        match Or::short(&a) {
            Some(v) => v,
            None => Or::or(a, $b),
        }
    }}
}

// ----

#[derive(Debug, Clone, Copy)]
enum Tri {
	False = -1,
	None = 0,
	True = 1,
}

impl And for Tri {
	type Output = Tri;
	fn short(&self) -> Option<Tri> {
		println!("  and-short({:?})", self);
		match *self {
			Tri::False => Some(Tri::False),
			_ => None,
		}
	}
	fn and(self, rhs: Tri) -> Tri {
		println!("  and({:?}, {:?})", self, rhs);
		match (self, rhs) {
			(Tri::False, _) |
			(_, Tri::False) => Tri::False,
			(Tri::None, _) |
			(_, Tri::None) => Tri::None,
			(Tri::True, Tri::True) => Tri::True,
		}
	}
}

impl Or for Tri {
    type Output = Tri;
    fn short(&self) -> Option<Tri> {
        println!("  or-short({:?})", self);
        match *self {
            Tri::True => Some(Tri::True),
            _ => None,
        }
    }
    fn or(self, rhs: Tri) -> Tri {
        println!("  or({:?}, {:?})", self, rhs);
        match (self, rhs) {
            (Tri::True, _) |
            (_, Tri::True) => Tri::True,
			(Tri::None, _) |
			(_, Tri::None) => Tri::None,
			(Tri::False, Tri::False) => Tri::False,
        }
    }
}

fn main() {
	for l in [Tri::False, Tri::None, Tri::True].iter().cloned() {
		for r in [Tri::False, Tri::None, Tri::True].iter().cloned() {
			println!("{:?} && {:?}", l, r);
			println!("  {:?}", and!(l, {
			    println!("  rhs evaluated");
			    r
			}));
			println!("{:?} || {:?}", l, r);
			println!("  {:?}", or!(l, {
			    println!("  rhs evaluated");
			    r
			}));
		}
	}
}