zarinfam

public class Main { 
 
    @FunctionalInterface 
    interface Function3 <A, B, C, R> { 
        public R apply (A a, B b, C c); 
    } 
 
    public static void main(String[] args) { 
        BiFunction<Integer, Integer, Integer> add = Math::addExact; 
        BiFunction<Integer, Integer, Integer> subtract = Math::subtractExact; 

zarinfam

interface Empty<A> {
    A empty();
}

zarinfam

class EmptyInt implements Empty<Integer>{
    @Override
    public Integer empty() {
        return 0;
    }
}

zarinfam

interface Empty<A> {
    A empty();

    static Empty<Integer> emptyInt(){
        return new EmptyInt();
    }
}

zarinfam

interface Empty<A> {
    A empty();

    static Empty<Integer> emptyInt(){
        return () -> 0;
    }
}

zarinfam

final class Functions {
    static <T> Tuple2<T, T> twoEmpties(Empty<T> empty) {
        return Tuple.of(empty.empty(), empty.empty());
    }
...
}

zarinfam

var xAndY = twoEmpties(emptyInt());
System.out.println("{" + xAndY._1() + ", " + xAndY._2() + "}");

zarinfam

val xAndY = twoEmpties()

zarinfam

interface Show<A> {
    String show(A a);

    static <X, Y> Show<Tuple2<X, Y>> showTuple() {
        return t -> "{" + t._1() + ", " + t._2() + "}";
    }
}

zarinfam

static <A> String show(A a, Show<A> sh) {
    return sh.show(a);
}