Re: [Caml-list] optional arguments

[Brian Hurt <bhurt@spnz.org>]

On Mon, 17 Nov 2003, Selentek 24331-03 wrote:

> Hello,
> 
> Is there any way to "send optional argument with None value".
> for example:
> 
> let a = None;;
> val a : 'a option = None

If you delete the above two lines...

> 
> let f ?v () =
>   match v with
>   | Some i -> i + 1
>   | None   -> 0
> 

This code just does what you want it to.  It has the type:
val f : ?v:int -> unit -> int = <fun>

And is called like:
f ();;  (* returns 0 *)
f ~v:1 () ;; (* returns 2 *)

Another possibility is to do:

let f ?(v = None) () =
    match v with
       None -> 0
       | Some i -> i + 1
;;

This has the type:
val f : ?v:int option -> unit -> int = <fun>

And is called like:
f ();; (* returns 0 *)
f ~v:None ();; (* returns 0 *)
f ~v:(Some 1) ();; (* returns 2 *)

Form #2 is probably want you want to do if you just want to pass in an 
option.

> 
> Sorry for my english.
> 

Your english is as good as mine :-}.

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Brian

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