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Fuck you. Stop asking time complexity or space complexity of functional code. No one fucking knows.

"functional code" code that works or code programmed in functional style?

@Demolishun functional style

I could see this being an issue with C++. gcc likes to take recursive functions and turn them into loops when compiling. So the space used would be small for stack variables. Which compiler used might make a difference.

@Demolishun if you're writing recursions you're doing something wrong already, no?

@iiii Some problems are easier to reason with recursion.

@Demolishun and are easy to remake into loops as well. Just add some fake stack and done.

@iiii
Actual functional languages do tail call optimization. Tail-recursive functions are compiled as loops there.

In such functional languages, you are allowed to write a recursive solution as a tail-recursive function. You don't need to convert it to a loop by hand.
And sometimes a recursive solution is easier to read and understand.

@iiii I'm very interested in how that works. Can you show me an example
with the classical filesystem traversal problem?

@Oktokolo and C++ is not a functional language. It can do some recursion optimisation but no one should rely on that, because it's actually not a defined feature of the language, as far as I am aware

@hjk101 what is the definition of it?

How can you not get time complexity from functional code?

@iiii https://rosettacode.org/wiki/...
Or pick any other language example with a recursive walk function actually visible.

@hjk101
1. scan current directory.
2. Print all files.
3. Add all subdirectories to a list.
4. Take the first directory in a list and remove it from the list
5. Apply everything from 1 to this directory
6. Repeat until the list is empty.

@iiii thanks didn't know what you meant with fake stack but makes sense now.
I was thinking along the same lines with building an itterable datastructure.

@hjk101 anything that can hold intermediate values in the way you need

@iiii good luck trying to parse languages without using recursion.

Doable? Maybe.
Maintainable? No way.

@GeorgeBool I find some problems are much easier to reason about with recursion. Also, why spend the time making it non-recursive? If you structure it with a tail call the compiler can do whatever it likes with the code. The place I use it the most is trees.

@bioDan for parsing languages no one sane uses recursive functions but parsers based on automatons and grammar...

@iiii which are recursive.. if you are building a parser.