Incremental Function in Java

Delta.java

package fp.ilc;

import fj.F2;

public class Delta<A,DA> {
    private final F2<A,DA,A> _patch;
    private final DA _change;

    private Delta(F2<A,DA,A> patch, DA change) {
        this._patch = patch;
        this._change = change;
    }

    public F2<A, DA, A> patch() {
        return _patch;
    }

    public DA change() {
        return _change;
    }

    public A patch(A a) {
        return patch().f(a, change());
    }
}

IncF.java

package fp.ilc;

import fp.inc_f.IncFCartesian;
import fp.inc_f.IncFCategory;
import fp.inc_f.IncFSemigroupoid;
import fp.kinds.__;
import fp.kinds.__2;
import fj.P2;

public interface IncF<A,B> extends __2<IncF.Mu,A,B> {
    interface Mu {}

    static <A,B> IncF<A,B> narrow(__<__<Mu,A>,B> a) {
        return (IncF<A,B>)a;
    }

    P2<B,IncF2<A,B>> apply(A a);

    static IncFSemigroupoid semigroupoid() {
        return new IncFSemigroupoid() {};
    }

    static IncFCategory category() {
        return new IncFCategory() {};
    }

    static <U> IncFCartesian<U> cartesian() {
        return new IncFCartesian<U>() {};
    }
}

IncF2.java

package fp.ilc;

import fp.kinds.__;
import fp.kinds.__2;
import fj.P2;

public interface IncF2<A,B> extends __2<IncF2.Mu,A,B> {
    interface Mu {}

    static <A,B> IncF2<A,B> narrow(__<__<IncF2.Mu,A>,B> a) {
        return (IncF2<A,B>)a;
    }

    P2<Delta<B,?>,IncF2<A,B>> apply(Delta<A,?> delta);
}