Function canrun::goals::both

pub fn both<'a, D>(a: Goal<'a, D>, b: Goal<'a, D>) -> Goal<'a, D> where
    D: Domain<'a>, 

Create a goal that only succeeds if both sub-goals succeed.

This is essentially an “AND” operation. The resulting state will be the result of the combining the two sub-goals.

If the first goal fails, the second goal will not be attempted.

Examples

Two successful goals allow values to flow between vars:

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

let x = var();
let y = var();
let goal: Goal<I32> = both(unify(y, x), unify(1, x));
let result: Vec<_> = goal.query(x).collect();
assert_eq!(result, vec![1])

A failing goal will cause the entire goal to fail:

let goal: Goal<I32> = both(unify(2, x), unify(1, x));
let result: Vec<_> = goal.query(x).collect();
assert_eq!(result, vec![]) // Empty result