use std::fmt;
use std::fmt::Debug;
use std::rc::Rc;
use crate::goals::Goal;
use crate::{
constraints::{resolve_2, Constraint, ResolveFn, VarWatch},
core::{State, Unify, Value},
};
#[allow(clippy::type_complexity)]
pub struct Project2<A: Unify, B: Unify> {
a: Value<A>,
b: Value<B>,
f: Rc<dyn Fn(Rc<A>, Rc<B>) -> Box<dyn Goal>>,
}
pub fn project_2<A, IA, B, IB, F>(a: IA, b: IB, func: F) -> Project2<A, B>
where
A: Unify,
IA: Into<Value<A>>,
B: Unify,
IB: Into<Value<B>>,
F: Fn(Rc<A>, Rc<B>) -> Box<dyn Goal> + 'static,
{
Project2 {
a: a.into(),
b: b.into(),
f: Rc::new(func),
}
}
impl<A: Unify, B: Unify> Clone for Project2<A, B> {
fn clone(&self) -> Self {
Self {
a: self.a.clone(),
b: self.b.clone(),
f: self.f.clone(),
}
}
}
impl<A: Unify, B: Unify> Goal for Project2<A, B> {
fn apply(&self, state: State) -> Option<State> {
state.constrain(Rc::new(self.clone()))
}
}
impl<A: Unify, B: Unify> Constraint for Project2<A, B> {
fn attempt(&self, state: &State) -> Result<ResolveFn, VarWatch> {
let (a, b) = resolve_2(&self.a, &self.b, state)?;
let goal = (self.f)(a, b);
Ok(Box::new(move |state| goal.apply(state)))
}
}
impl<A: Unify + Debug, B: Unify + Debug> Debug for Project2<A, B> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Project2 {:?} {:?}", self.a, self.b)
}
}
#[cfg(test)]
mod tests {
use crate::{
core::{LVar, Query},
goals::{both::both, fail::Fail, project::project_2::project_2, succeed::Succeed, unify},
};
#[test]
fn succeeds() {
let x = LVar::new();
let y = LVar::new();
let goal = both(
both(unify(1, x), unify(2, y)),
project_2(x, y, |x, y| {
if x < y {
Box::new(Succeed)
} else {
Box::new(Fail)
}
}),
);
assert_eq!(goal.query(x).collect::<Vec<_>>(), vec![1]);
}
#[test]
fn fails() {
let x = LVar::new();
let y = LVar::new();
let goal = both(
both(unify(1, x), unify(2, y)),
project_2(x, y, |x, y| {
if x > y {
Box::new(Succeed)
} else {
Box::new(Fail)
}
}),
);
assert_eq!(goal.query(x).collect::<Vec<_>>(), vec![]);
}
}