Hi all, the question seems like a simple question, but it has thrown me for a long time. I have a loop in which I loop through an element of the map list and I need to add the current item to the new list. For a better understanding, here is a simpler example: current_list = [] for x <- 1..10 do c…

The current_list inside the for-loop is not the same variable as the current_list outside the for-loop. Actually, the current_list inside each loop is different. I bet you’ve heard that in Elixir, everything is immutable, which means if a list is empty, it stays empty for the rest of its life. You …

or simply :slight_smile: current_list = Enum.reduce(1..10, [], fn x, acc -> [x | acc] end)

I guess the author may have put something in the current_list before starting the loop :slight_smile: If the current_list is initially empty, then Enum.reverse(1..10) should be the shortest code.

IMHO, newbies should stay away from if, for or with until being comfortable with functional style programming. They are only syntactical sugar to make things shorter; they don’t provide any vital functionalities.

IDK, if is such a common core construct it feels like it would be off-putting to try to learn a lang where that was discouraged. In fact I’d say it’s the ideal candidate from which to learn this functional scoping lesson!

[image] christhekeele: learn this functional scoping lesson Lexical scoping isn’t limited to functional languages. Many languages use that type of scoping. Usually people don’t expect do/end blocks to be scope boundries though.

[image] LostKobrakai: Usually people don’t expect do/end blocks to be scope boundries though. Right! The combination of lexical scoping, expression return values, resulting in do/end variables being local and needing to assign out of them, is what’s the useful take-away. I think if is great …

A cond do ... will raise if none of the conditions hold true. This is safer for newbies than if that don’t have a else clause.

[image] LostKobrakai: Lexical scoping isn’t limited to functional languages. Many languages use that type of scoping. Yes, though paired with immutability and implicit shadowing it is sometimes a bit weird. foo = 0 if true, do: foo = 1 IO.puts(foo) If you do not know about the implicit shad…

I suppose the compiler could warn on reassignment of shadowed variables. There are legitimate use-cases for it though, especially in more involved conditional bodies. Especially in reduces!

The compiler would certainly warn on the example above because “foo” is unused.

Elixir Programming Language Forum

Changing variables in a loop

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kokolegorille November 1, 2021, 9:35am 3

or simply

current_list = Enum.reduce(1..10, [], fn x, acc ->
  [x | acc]
end)