[Caml-list] optional arguments

[Caml-list] optional arguments

[Selentek 24331-03]

Hello,

Is there any way to "send optional argument with None value".
for example:

let a = None;;
val a : 'a option = None

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

.

First solution:

match a with
| Some i -> f ~v:i ()
| None   -> f ()

Can I find something more easy with out redifinition of the function ?
something like: f a (), but funtion defined by ``let f ?v'' and ``a'' is int option.


Thanks.

Sorry for my english.
-- 

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Re: [Caml-list] optional arguments

[Richard Jones]

On Mon, Nov 17, 2003 at 11:52:49AM +0300, Selentek 24331-03 wrote:
[...]

Like this?

# let f ?v () =
  match v with
  | Some i -> i + 1
  | None   -> 0      ;;
val f : ?v:int -> unit -> int = <fun>

# let v = Some 1;;
val v : int option = Some 1

# f ?v ();;
- : int = 2

# let v = None;;
val v : 'a option = None

# f ?v ();;
- : int = 0

Rich.

-- 
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Merjis Ltd. http://www.merjis.com/ - improving website return on investment
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Re: [Caml-list] optional arguments

[Artem Prisyznuk]

On Mon, 17 Nov 2003 11:52:49 +0300, Selentek 24331-03 <epifanov@komset.ru> 
wrote:

> Is there any way to "send optional argument with None value".

f ?v:a ();;


> let a = None;;
> val a : 'a option = None
>
> let f ?v () =
>   match v with
>   | Some i -> i + 1
>   | None   -> 0



-- 
Artem Prysyznuk
tema@sit.kiev.ua

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Re: [Caml-list] optional arguments

[Selentek 24331-03]

YES! Thanks for information.

On 10:13 Mon 17 Nov     , Richard Jones wrote:
> On Mon, Nov 17, 2003 at 11:52:49AM +0300, Selentek 24331-03 wrote:
> [...]
> 
> Like this?
> 
> # let f ?v () =
>   match v with
>   | Some i -> i + 1
>   | None   -> 0      ;;
> val f : ?v:int -> unit -> int = <fun>
> 
> # let v = Some 1;;
> val v : int option = Some 1
> 
> # f ?v ();;
> - : int = 2
> 
> # let v = None;;
> val v : 'a option = None
> 
> # f ?v ();;
> - : int = 0
> 
> Rich.
> 
> -- 
> Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
> Merjis Ltd. http://www.merjis.com/ - improving website return on investment
> MONOLITH is an advanced framework for writing web applications in C, easier
> than using Perl & Java, much faster and smaller, reusable widget-based arch,
> database-backed, discussion, chat, calendaring:
> http://www.annexia.org/freeware/monolith/

-- 
Gentoo Linux http://www.gentoo.org

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Re: [Caml-list] optional arguments

[Brian Hurt]

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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Re: [Caml-list] Optional arguments

[malc]

On Sun, 9 Nov 2008, David Teller wrote:

> What were you expecting?
>
> Your definition of [a] always passes argument [i] to [b], so the default
> value is never used.

Yes indeed, i probably should quit writing code this late, sorry for
the noise.

-- 
mailto:av1474@comtv.ru

Re: [Caml-list] Optional arguments

[David Teller]

What were you expecting?

Your definition of [a] always passes argument [i] to [b], so the default
value is never used.

Cheers,
 David

On Sun, 2008-11-09 at 22:17 +0300, malc wrote:
> Objective Caml version 3.10.0
> 
> # let a i = let b ?(i=i mod 3) () = i in b ~i ();;
> val a : int -> int = <fun>
> # for i = 0 to 5 do print_int (a i); done;;
> 012345- : unit = ()
> 
> Is this something to be expected? Or perhaps something which calls
> for an upgrade?
> 
-- 
David Teller-Rajchenbach
 Security of Distributed Systems
  http://www.univ-orleans.fr/lifo/Members/David.Teller
 Angry researcher: French Universities need reforms, but the LRU act brings liquidations.