what does something like this do (t ++ [d]) and why use [d] instead of d and finally, why the parentheses… unfortunately the code is not documented as it seems that if you cain't read ELIXIR, you cain.t read.... so documentation ain't needed. thank you for your help.

Hi, it is a merge of 2 lists: you append the list [d] (a list of one element, d) to t which is a list. There are several ways to write the same thing (for example: List.insert_at(t, -1, d)) why the parentheses… Can’t say without the rest of the code. To avoid a conflict (precedence) with an oth…

if t and d are lists then why use [d] instead of d since t does not have the brackets [[] ???

Kernel.++/2 only works with lists as arguments. t ++ d won’t work (not exactly, you’ll end with an improper list) EDIT: [image] dorgan: That’s partially correct. Yeah, I was editing my post at the same time and hesitate if, for the PO, this “detail” would be confusing and worths mentioning…

d needs to be wrapped in a list if it’s a single element, otherwise you’ll end up with an improper list [1, 2, 3 | d] I go over the fine details here: Making sense of Elixir (improper) lists (dorgan.ar) . The tl;dr is that is has to do with the way lists are constructed. [1, 2, 3] is actually [1 | […

this is the complete function: defp add_when_in(t, k, l, d) do if k in l do (t ++ [d]) else t end end

Thank you for all of your answers, it’s amazing how a simple list can complicate matters depending on how it’s used. in my case it was the naming convention or the lack of it that threw me for a loop. Thanks guys not only for clear and prompt description but for being there. Now I can apply this n…

when testing the [] ++ :wut I get: LC-210722 inside add_when_in with ([] ++ :wut) lists LC-210712 my data: :wut so now, what does this mean? Thanks again PS: I am reading the article: Making sense of Elixir (improper) lists (dorgan.ar) .

The ++ operator looks for the last [] in the list and replaces it with the value at the right side without checking if it’s also a list. So if you give it [] at the left, it will “replace” it with the value at the right, so you get the right side value and no list.

humm, food for thought, will play with this a bit more… thanks again,

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What does something like this (t ++ [d]) do

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t0t0 July 22, 2021, 3:01pm 8

You were right, parentheses are not required here.