Investigate Data unification

[mlhaufe]

Unification is currently implemented as a part of pattern matching in traits.

What if this was lifted into something more first class? What would it enable?

example:

const Point2 = Data({x: Number, y: Number})

const pt1 = Point2(12, _),
    pt2 = Point2(_, 3)

const pt3 = unify(pt1, pt2)

pt3 === Point2(12, 3)

[mlhaufe]

With lazy fields this opens up even more interesting possibilities:

const foo = S({ left: _, right: () => foo })

Is there some logic programming functionality this enables?

[mlhaufe]

Interestingly, Flix has an embedded Datalog:

def reachable(g: List[(String, Int32, String)], minSpeed: Int32): List[(String, String)] =
    let facts = inject g into Road;
    let rules = #{
        Path(x, y) :- Road(x, maxSpeed, y), if maxSpeed >= minSpeed.
        Path(x, z) :- Path(x, y), Road(y, maxSpeed, z), if maxSpeed >= minSpeed.
    };
    query facts, rules select (src, dst) from Path(src, dst) |> Foldable.toList

let p = #{
    /// Parts and the components they depend on.
    PartDepends("Car",       "Chassis").
    PartDepends("Car",       "Engine").
    PartDepends("Engine",    "Piston").
    PartDepends("Engine",    "Ignition").

    /// Time required to assemble a part from its components.
    AssemblyTime("Car",     7).
    AssemblyTime("Engine",  2).

    /// Expected delivery date for certain components.
    DeliveryDate("Chassis";  2).
    DeliveryDate("Piston";   1).
    DeliveryDate("Ignition"; 7).

    /// A part is ready when it is delivered.
    ReadyDate(part; date) :-
        DeliveryDate(part; date).

    /// Or when it can be assembled from its components.
    ReadyDate(part; assemblyTime + componentDate) :-
        PartDepends(part, component),
        AssemblyTime(part, assemblyTime),
        ReadyDate(component; componentDate).
};

// Computes the delivery date for each component.
let r = query p select (c, d) from ReadyDate(c; d)