[tsss]

Your FP example is needlessly complicated. No one who does FP regularly would write it like that.

  var favoriteFoodsOfFurryPetsOfFamousAuthorsOfLongChineseBooksAboutHistory = books
    .filter(book => 
       book.pageCount > 100 and 
       book.language == "Chinese" and 
       book.subject == "History" and
       book.author.mentions > 10_000
    )
    .flatMap(book => book.author.pets)
    .filter(pet => pet.is_furry)
    .map(pet => pet.favoriteFood)
    .distinct()

Or in Scala:

  val favoriteFoodsOfFurryPetsOfFamousAuthorsOfLongChineseBooksAboutHistory = (for {
    book <- books if
      book.pageCount > 100 &&
      book.language == "Chinese" &&
      book.subject == "History &&
      book.author.metnions > 10_000
    pet <- book.author.pets if
      pet.is_furry
  } yield pet.favoriteFood).distinct

Though, most Scala programmers would prefer higher-order functions over for-comprehensions for this.

[Chris_Newton]

I didn’t see the original, but the FP example here looks fairly idiomatic to me.

An alternative, which in FP-friendly languages would have almost identical performance, would be to make the shift in objects more explicit:

    var favoriteFoodsOfFurryPetsOfFamousAuthorsOfLongChineseBooksAboutHistory =
      books
        .filter(book => isLongChineseBookAboutHistory(book))
        .map(book => book.author)
        .filter(author => isFamous(author))
        .flatMap(author => author.pets)
        .filter(pet => pet.isFurry)
        .map(pet => pet.favouriteFood)
        .distinct()

I slightly prefer this style with such a long pipeline, because to me it’s now built from standard patterns with relatively simple and semantically meaningful descriptions of what fills their holes. Obviously there’s some subjective judgement involved with anything like this; for example, if the concept of an author being famous was a recurring one then I’d probably want it defined in one place like an `isFamous` function, but if this were the only place in the code that needed to make that decision, I might inline the comparison.

[itsmeknt]

Thanks! I have updated my post to use your code. It is indeed much nicer. And yes, I don't write much FP.

I just improved the comprehension code as well using the same idea as your code, eliminating an entire list!