I believe the mailing list is the correct place for these sorts of suggestions.
adamu
krasenyp
I really don’t see the reason for a raising version. When the list is empty then there’s no first or last element so nil is exactly what I’d expect. I’d even argue that a non-empty list is a separate data structure because we can’t express the constraint in the type system.
0
NobbZ
On a not statically typed language, where we can’t distinguish the default nil from a real nil that was in the list, I hate that I have to build my own stuff around it, by matching on the list first, rather than relying on the stdlib.
Code like the following is something I often have in my projects.
def first([]), do: {:error, :empty}
def first(l), do: {:ok, List.first(l)}
I prefer a matchable variant over a raising one though.
1
josevalim
Creator of Elixir
We have recently discussed it here: Typing lists and tuples in Elixir - The Elixir programming language
The idea is that hd will require a non-empty list to be given as argument (so in statically typed code you won’t get a runtime failure), while a potential List.first! and List.last! will imply a runtime error if an empty list is given (hence the bang). Given we were already planning to have those, please go and submit a PR, although I’d say it is also desirable to speed up Enum.fetch!(list, -1).
I’d say it is redundant to have List.first (or similar) that return a tuple given you can directly match on the list instead:
case List.fetch_first(list) do
{:ok, first} -> first
:error -> ...
end
vs
case list do
[first | _] -> first
[] -> ...
end
The second case is simpler, faster and clearer (IMO). So the List.first should either return a default (so you can skip the case) OR raise. The tuple case is not valuable.
4
lud
@pierrelegall @jswanner the post I respond to specifically shows 0 arity functions. Probably a formatting error and not the actual code.
Otherwise on the topic I don’t really see the point of List.first!. Isn’t hd commonly known and used?
0
lpil
Creator of Gleam
That’s great!
Would the type of List.last be (excuse my pseudocode) fn(non_empty_list(element)) → element | fn([]) → nil? And then the compiler would warn you if you forget to handle the empty list case?
0
pierrelegall
The PR has been merged into Elixir main branch.
6
