Function canrun::goals::project::project_2

pub fn project_2<'a, A, AV, B, BV, D, F>(a: AV, b: BV, func: F) -> Goal<'a, D> where
    A: Debug + 'a,
    AV: IntoVal<A>,
    B: Debug + 'a,
    BV: IntoVal<B>,
    D: DomainType<'a, A> + DomainType<'a, B>,
    F: Fn(Rc<A>, Rc<B>) -> Goal<'a, D> + 'a, 

Create a projection goal that allows creating a new goal based on the resolved values.

use canrun::{Goal, all, unify, var, project_2};
use canrun::example::I32;

let (x, y) = (var(), var());
let goal: Goal<I32> = all![
    unify(1, x),
    unify(2, y),
    project_2(x, y, |x, y| if x < y { Goal::succeed() } else { Goal::fail() }),
];
let result: Vec<_> = goal.query((x, y)).collect();
assert_eq!(result, vec![(1, 2)])