class Book {
  private final Genre genre;
  private final String author;
  private final String title;
  private final LocalDate publicationDate;

  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    Book book = (Book) o;
    return Objects.equals(author, book.author)
            && Objects.equals(genre, book.genre)
            && Objects.equals(title, book.title)
            && Objects.equals(publicationDate, book.publicationDate);
  }

  @Override
  public int hashCode() {
    return Objects.hash(author, genre, title, publicationDate);
  }

  @Override
  public String toString() {<FILL_FUNCTION_BODY>}

  /**
   * Curried book builder/creator function.
   */
  static Function<Genre, Function<String, Function<String, Function<LocalDate, Book>>>> book_creator
      = bookGenre
          -> bookAuthor
              -> bookTitle
                  -> bookPublicationDate
                      -> new Book(bookGenre, bookAuthor, bookTitle, bookPublicationDate);

  /**
   * Implements the builder pattern using functional interfaces to create a more readable book
   * creator function. This function is equivalent to the BOOK_CREATOR function.
   */
  public static AddGenre builder() {
    return genre
        -> author
            -> title
                -> publicationDate
                    -> new Book(genre, author, title, publicationDate);
  }

  /**
   * Functional interface which adds the genre to a book.
   */
  public interface AddGenre {
    Book.AddAuthor withGenre(Genre genre);
  }

  /**
   * Functional interface which adds the author to a book.
   */
  public interface AddAuthor {
    Book.AddTitle withAuthor(String author);
  }

  /**
   * Functional interface which adds the title to a book.
   */
  public interface AddTitle {
    Book.AddPublicationDate withTitle(String title);
  }

  /**
   * Functional interface which adds the publication date to a book.
   */
  public interface AddPublicationDate {
    Book withPublicationDate(LocalDate publicationDate);
  }
}

    return "Book{" + "genre=" + genre + ", author='" + author + '\''
            + ", title='" + title + '\'' + ", publicationDate=" + publicationDate + '}';
  
<no_super_class>