Trait ukanren::Goal[−][src]

pub trait Goal {
    type Iter: Iterator<Item = State>;
    fn apply(&self, s: &State) -> Self::Iter;

    fn and<G, I>(self, other: G) -> And<Self, G>
    where
        Self: Sized,
        G: Goal<Iter = I>,
        I: Iterator<Item = State>,
    { ... }

    fn or<G, I>(self, other: G) -> Or<Self, G>
    where
        Self: Sized,
        G: Goal<Iter = I>,
        I: Iterator<Item = State>,
    { ... }

    fn boxed(self) -> BoxedGoal<Self::Iter>
    where
        Self: Sized + 'static,
    { ... }

    fn run(&self, k: usize) -> RunStream<Self::Iter> { ... }
}
Expand description

A goal that can be executed by the relational system.

Associated Types

The state iterator returned by the goal.

Required methods

Apply this goal to an initial state, returning a stream of satisfying states.

Provided methods

Take the conjunction of this goal with another.

Example

use ukanren::{eq, fresh, Goal};

// Goal where `x` is equal to `5` and `y` is equal to `6`.
fresh(|x, y| eq(&x, &5).and(eq(&y, &6)));

Take the disjunction of this goal with another.

Example

use ukanren::{eq, fresh, Goal};

// Goal where `x` is equal to `5` or `x` is equal to `6`.
fresh(|x| eq(&x, &5).or(eq(&x, &6)));

Box this goal into a trait object, making it easier to name the type.

Example

use ukanren::{eq, BoxedGoal, Goal, Value, State};

fn animalo(x: Value) -> BoxedGoal<impl Iterator<Item = State>> {
    eq(&x, &"dog").or(eq(&x, &"cat")).boxed()
}

Evaluate this goal on an empty state, returning a stream of results.

These results contain normalized forms of the first k variables, to avoid including auxiliary data that is not relevant to us.

This is a low-level function. Instead of calling this function directly, you should probably use the top-level run function instead, which infers the value of k from your input.

Implementors