(Assuming atp means 'at this point')

Hm, I am not sure. Maybe? :) But there will always be three elements to concatenate on every line.

I personally try to avoid lambdas (unless needed for higher order functions), but that is a matter of taste.

why not using lambda and join atp? (i don't know if it's actually possible, but i think it should be just by looking at how you used the return)

Did this lmao

You are correct. =) But I solve katas for fun, and sometimes that goes against best practises.

Putting the whole function in one line may be clever, but it's not best practices.