Re: testing keyboard input for a digit

On 10/24/2013 08:35 AM, Jean Saint-Remy wrote:
> Hi,
>
> I am trying to test user's input to see if it contains a digit, but it
> is not going so well
>
> let rec kbd () =
>    let ls = [0;1;2;3;4;5;6;7;8;9;] (* there doesn't seem to be a way of
> expressing a range 0..9 *)

Consider using the batteries included library for any real project.

http://ocaml-batteries-team.github.io/batteries-included/hdoc2/

>    let rec find test = function
>      | [] -> raise Not_found
>      | hd :: tl -> if test hd then hd else find test tl in
>         print_string "Please enter an item number: ";
>         try
>            let item = read_line () in
>            if (item = find ls) then failwith "an item should contain a
> digit ";
>            item
>       with Failure msg -> (print_endline (msg ^ ", try again"); kbd ()) ;;
>
> -: Error This expr "ls" has type int list but an expression was expected
> of type 'a -> bool
>
> Thank you for any suggestion

You can use Scanf.sscanf to convert a string to a number.

http://ocaml-batteries-team.github.io/batteries-included/hdoc2/BatScanf.html

You can catch the scan failure to ask the user to try again.

Here are some trials in the toplevel:

let item = "10" in
Scanf.sscanf item "%d" (fun i -> i);;

let item = "toto" in
   Scanf.sscanf item "%d" (fun i -> i);;
Exception:
Scanf.Scan_failure
  "scanf: bad input at char number 0: ``character 't' is not a decimal 
digit''".

Have fun,
F.

> jean
>
> 


-- 
Best regards,
Francois Berenger.


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