CharlesO
Erlang :list.nth simple, but 1 - based
nth(1, [H|_]) -> H;
nth(N, [_|T]) when N > 1 ->
nth(N - 1, T).
Elixir Enum.at … cool, but not focused on Lists
def at(enumerable, index, default \\ nil) do
case fetch(enumerable, index) do
{:ok, h} -> h
:error -> default
end
end
...
# other code to check if _is a list_ or not, before redirtecting to do_fetch...
Elixir could (should?) have List.nth, a 0-based equivalent of Erlang’s :list.nth that expects to work only on lists (nth could even make it into the kernel 
)
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michalmuskala
The
Enum,fetch/2thatEnum.at/2uses has a clause that is specialised for lists, so it should be as efficient as the Erlang’s:lists.nth/2without introducing extra functions.https://github.com/elixir-lang/elixir/blob/master/lib/elixir/lib/enum.ex#L2773-L2778
NobbZ
Also nomenclature forbids zero basing nth. There is no element before the first.
CharlesO
I don’t follow your argument
NobbZ
Well by writing List.nth(list, 0), you do request the element right before the first one.
There is never a zeroth item. You always start with the first. When one calls the function nth, he has to start counting with 1.
CharlesO
Doesn’t
Enum.at/2contradict what you are saying?Enum.at list, 0sztosz
It’s a language (any language english, polish, german, whatever) trait. There can not 0th element, how would you call it? Zeroth? You have to start count from 1 (one), so → First, Second, Third, Fourth … Nth element. There is simply no Zeroth element
It would be illogical.
On the other hand something can be at position marked as 0, zero. Something before it is at position 1 relative to position 0, and something behind is at position -1 (also relative to that 0 position). Or the other way round, based on do you want position number before or after that position. And element on position 1 is first from from, but that does not mean you’re “zeroth” from you.
Of course first element from the beginning of the list would be that at position 0, but then we would meant that we have to remember that nth element is on position n - 1. At that can lead to subtle off by 1 errors I would rather avoid.
In Erlang
Unless otherwise stated, all functions assume that position numbering starts at 1but in elixir we start at 0, hence having List.nth does not make, sadly, too much senseminhajuddin
I disagree
0thseems very logical if you think of it as a position. If that doesn’t make sense then how does nth make sense? You could even sayEnum.atshows thenthelement in a list wherenis a position.sztosz
Can use a word to describe that position?
Onor.io
Why add a new function which can be easily done in just the fashion that @michalmuskala outlines above?
peerreynders
“0” is logical as an item offset when applied to a number of data type instances (of equal size), stored in a contiguous area of memory - what is typically thought of as an array.
In C this goes back to pointer arithmetic:
arr[i] == *(arr + i)- this “index” syntax has been basically grandfathered into it’s various descendants and derivatives.nis at offsetn-1forn > 0In functional programming languages “List” typically refers to a “Linked List”. In a linked list the items aren’t (usually) adjacent in memory so an offset isn’t as useful for “Lists”. Now
Enum.atandEnum.fetchadopted the familiar 0-based index - in a sense that “index” is describing the “distance” into the enumeration starting at item 1 - i.e. item 1 is found at “distance” 0 from item 1 (rather than 0 being a “position”).