import io.vavr.Function1;
import io.vavr.Tuple;
import io.vavr.Tuple2;
import io.vavr.collection.List;
import io.vavr.Option;

import static io.vavr.collection.List.unfoldRight;

class A {}
class B {}
class Main {
    Function1<A, Option<Tuple2<B, A>>> f = (a) -> Option.of(Tuple.of(new B(), new A()));
    List<B> L0 = unfoldRight(new A(), f); // *
    List<B> L1 = unfoldRight(new A(), (a) -> Option.of(Tuple.of(new B(), new A()));

    Option<Tuple2<B, A>> g(A a) { return Option.of(Tuple.of(new B(), new A())); }
    List<B> L2 = unfoldRight(new A(), (a) -> g(a)); // **
}


// *  Compilation fails with: "Incompatible equality constraint: ? extends T and A"

// ** Compilation fails with: "Incompatible equality constraint: ? extends A and A"

static <T, U> List<U> unfoldRight(T seed, Function<? super T, Option<Tuple2<? extends U, ? extends T>>> f)