Bind/Flat map nested stream

BindNestedStreamSample.java

import lombok.extern.slf4j.Slf4j;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static java.lang.String.format;
import static java.util.Arrays.asList;

@Slf4j
public class BindNestedStreamSample {
    public static void main(String[] args) {

        List<ClassA> aLists = asList(
                new ClassA("1",
                        asList(
                                new ClassB("a", asList(
                                        new ClassC("I"))))),
                new ClassA("2",
                        asList(
                                new ClassB("a", asList(
                                        new ClassC("I"),
                                        new ClassC("II")
                                ))))
        );

        System.out.println("Imperative collect: "+imperativeCollect(aLists));
        System.out.println("Declarative collect: "+declarativeCollect(aLists));
    }

    private static List<String> imperativeCollect(List<ClassA> aList){
        List<String> strings = new ArrayList<>();
        for (ClassA a: aList){
            for(ClassB b: a.bList){
                for(ClassC c: b.cList) {
                    String string = stringify(a).apply(b).apply(c);
                    strings.add(string);
                }
            }
        }

        return strings;
    }

    private static List<String> declarativeCollect(List<ClassA> aList){
        return bindNestedStream(BindNestedStreamSample::stringify)
                .apply(aList.stream())
                .apply(a -> a.bList.stream())
                .apply(b -> b.cList.stream())
                .collect(Collectors.toList());
    }

    private static Function<ClassB, Function<ClassC, String>> stringify(ClassA a){
        return b -> c -> format("%s-%s-%s", a.name, b.name, c.name);
    }

    //flattening nested streams with reference to parent. A comprehension pattern
    //equivalent to
    //
    //Stream aStream;
    //Stream bStream = a -> stream(a)
    //Stream cStream = b -> stream(b)
    //
    //for(A a: aStream){
    //   for(B b: bStream(a)){
    //      for(C c: cStream(b)){
    //          f(a, b, c)
    //      }
    //   }
    //}
    private static <A, B, C, D> Function<Stream<A>,
            Function<Function<A, Stream<B>>,
                    Function<Function<B, Stream<C>>, Stream<D>>>> bindNestedStream(
            Function<A, Function<B, Function<C, D>>> f) {

        return a -> b -> c ->
                a.flatMap(x ->
                        b.apply(x).flatMap(y ->
                                c.apply(y).map(z ->
                                        f.apply(x).apply(y).apply(z)
                                )
                        )
                );
    }

    private static class ClassA {
        private final String name;
        final List<ClassB> bList;

        private ClassA(String name, List<ClassB> bList) {
            this.name = name;
            this.bList = bList;
        }
    }

    private static class ClassB {
        private final String name;
        final List<ClassC> cList;

        private ClassB(String name, List<ClassC> cList) {
            this.name = name;
            this.cList = cList;
        }
    }

    private static class ClassC {
        private final String name;

        ClassC(String name) {
            this.name = name;
        }
    }

}