I'm trying to figure out the pros/cons of using a Loop/Helper function to handle the recursion in a CF

Specifically, are there

1. speed or
   
   
2. upper limit
   

benefits to using a "helper" or "looper" function instead of combining all the steps into a single or is that simply for readability?

What about using the CustomList function to handle the recursion?

I am not aware of any benefits (or drawbacks) other than using "dummy" parameters that one doesn't wish to expose in the calling calculation.

I would have thought that using a helper function for any looping calculation would make the overall calculation non-tail recursive, and therefore limit the function to the smaller ~10,000 recursion limit. A test I tried just now proved me wrong. I consider the benefit of not exposing "dummy" parameters a big deal, but I prefer to use variables to pass data up and down the function call stack rather than parameters for a helper function. See one of my UUID functions for an example. This can make the calculation more complicated, but it also means the function I write has no dependencies, which is helpful when copying useful functions a la carte between files.

Well, the thing about $variables is that their scope is much larger than the custom function itself - so one has to be absolutely sure a similarly named variable is not declared elsewhere. That's not so easy to achieve, esp. when one is copying functions across files.

Thank you both very much for your insight. Jeremy, I just looked at your UUID function and I really like the structure you've used. I plan on adapting my calculations to match it.

Variable management for custom function is indeed important to be very careful about. I accomplish it with a combination of a naming convention and hygienic code. When I use variables for passing data between iterations of a function, I always name the variable something like "$~ABC.variable", where "ABC" is a mini-namespace for the function or a collection of functions, and the tilde "~" is a convention for marking the variable as "private" even though FileMaker doesn't enforce such security. To be extra rigorous (and verbose), you could just use the full name of the function. I also make sure to null-out any such variables in a garbage collection step at the end of a function to avoid unintended side effects (unless those variables are used to share information between different functions). I stick to local $variables rather than global $$variables when possible to minimize the scope of any variable I neglect to purge.

It can seem like a lot to keep track of, but I think it's worth it — obviously, since I do it. It's easier to keep track of when you're used to it. I wont always do this sort of thing for simpler functions due to the performance overhead of the structure you see in that UUID function; but I like having it in my toolbox.