Sure there is, the end tag of the list ] follows it. 
To me a comma at the end of an item means that item is ‘terminated’ in the listing. It is a separator when used on a single line, a terminator when on multi-line.
This is like in OCaml, do you do a prefix | or not? I.E. would you do a match like this:
match blah with
1 -> "1"
| 2 -> "2"
| 3 -> "3"
| _ -> "?"
Or would you do it like this?
match blah with
| 1 -> "1"
| 2 -> "2"
| 3 -> "3"
| _ -> "?"
The | is a case separator, it technically should not be before the first one, you can even write it like this just fine either way:
match blah with 1 -> "1" | 2 -> "2" | 3 -> "3" | _ -> "?"
match blah with | 1 -> "1" | 2 -> "2" | 3 -> "3" | _ -> "?"
Yet most people will write it with a prefix | on the first one when multiline and without a prefix | on a single line. Same thing when writing , on the last line in a list of elements as well, or rather a ; is a list separator in OCaml:
(* Single line *)
let some_list = [1; 2; 3; 4]
(* Multi line *)
let some_list = [
1;
2;
3;
]
You can of course do it backwards if you so wish though I rarely see this done:
(* Single line *)
let some_list = [1; 2; 3; 4;]
(* Multi line *)
let some_list = [
1;
2;
3
]
