Comment by s-zeng

2 days ago

Even in the world of functional programming, there's an argument to be made that `fold` is a bit of a code smell, in a similar vein as `while` being slightly smelly in an imperative code base. There's good reasons for each to be used, but they are such low level iteration primitives that you might be better off with a higher one (e.g. for loops or iterators in imperative programs; in FP you might reach for monoidic reduces (as opposed to folds where the accumulator is a different type from the list element), monadic traverses, or recursion schemes). Even though you can implement iterators or for loops in terms of while loops, you probably shouldn't, and similar for functional traversals.

In languages like python or Java though, you don't really have access to many of the higher power functional traversals however. So that puts you into a similar kind of bind as working in a language with only while loops

6 comments

s-zeng

Reply
nextaccountic  3 hours ago

> or recursion schemes

Fold is a recursion scheme

More complicated recursion schemes are progressively harder to read. Probably not great if you are not doing code golf

grebc  17 hours ago

I’ve never ever heard while described as a smell, or even slightly smelly.

Care to explain?

  • theamk  17 hours ago

    I assume OP refers to the cases where "while" is used to re-implement existing operations... imagine finding code like this:

         i = 0
     while i != len(todo):
         process(todo[i])
         i = i + 1

    sure, there may be a good reason to implement things this way (maybe "todo" grows during iteration?), but maybe not, and then the loop should be instead simplified to:

         for value in todo:
         process(value)

    (as an aside, this is exactly the case where the comments are required: "# not using for loop because todo might grow" will make it clear it's an intentional decision and not hallucination or something written from ignorance)

    • grebc  16 hours ago

      You can use iterators in a while loop like your for example, making it look as clean as the for.

      I feel like this is a case of personal preference over actual issue.

  • d--b  8 hours ago

    Probably because while is the source of many infinite loops, and because it’s sometimes faster and more rigorous to compute the length ahead of going into the loop.

    That said, I personally don’t think it’s smelly at all.