“选项列表”和“列表”之间的OCaml区别

Question

I got the following results when typing this function into the OCaml toplevel. The input appears to be identical to me both times, other that the whitespace surrounding the :: operator. Can anyone explain the difference between 'a option list and 'a option here?

# let rec at i = function
  | [] -> None
  | h::t -> if i = 1 then Some h else at (i-1) t;;
    val at : int -> 'a option list -> 'a option = <fun>
# let rec at i = function
  | [] -> None
  | h :: t -> if i = 1 then Some h else at (i-1) t;;
    val at : int -> 'a list -> 'a option = <fun>

Answer 1

Here's what I see:

$ ocaml
        OCaml version 4.01.0

# let rec at i = function
  | [] -> None
  | h::t -> if i = 1 then Some h else at (i-1) t;;
val at : int -> 'a list -> 'a option = <fun>
# let rec at i = function
  | [] -> None
  | h :: t -> if i = 1 then Some h else at (i-1) t;;
val at : int -> 'a list -> 'a option = <fun>

In my opinion, your experiment was flawed in some way. The spacing around :: isn't going to make any difference.