Re: what is the difference here ?

Hi,

When you write x :: y, it means that x represent the head of the list and y
represents the tail of the list, which is itself a list.
So x :: y and _ :: xs represent the same pattern, that's why you are
getting this warning.

You can read the following tutorial to understand the syntax about lists:
http://ocaml.org/learn/tutorials/data_types_and_matching.html

Cheers,

Esther Baruk

On Wed, Nov 5, 2014 at 3:28 PM, Roelof Wobben [email protected]
[ocaml_beginners] <[email protected]> wrote:

>
>
> Hello,
>
> I found the solution to exercise 2 of the 99 ocaml problems.
> The solution I found was this :
>
> let rec last_two list =
> match list with
> | [] | [_] -> None
> | [x;y] -> Some (x,y)
> | _::xs -> last_two xs ;;
>
> Now I wonder something.
> For me it looks like [x;y] and _::xs are the same.
> If I understand it right you can write [x;y] as x::y and _::xs looks
> then the same to me.
> But if I change [x;y] to x::y then I see a message that _:xs is not used.
>
> Can someone explain in simple words what is the difference between those
> two ?
>
> Roelof
>
>  
>