From: Dustin Sallings <dustin@spy.net>
To: "chris.danx" <chris.danx@ntlworld.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Closure & Ref
Date: Mon, 17 Nov 2003 13:02:32 -0800 [thread overview]
Message-ID: <5CBC9D22-1941-11D8-BBC4-000393CFE6B8@spy.net> (raw)
In-Reply-To: <3FB92396.4060908@ntlworld.com>
On Nov 17, 2003, at 11:37, chris.danx wrote:
> let prodAdd x =
> let value = ref x in
> fun y -> !value + y;;
This is very similar to
let prodAdd x y = x + y;;
The only difference is that I'm making a reference with the value of x.
# let prodAdd x = let value = ref x in fun y -> !value + y;;
val prodAdd : int -> int -> int = <fun>
# let prodAdd2 x y = x + y;;
val prodAdd2 : int -> int -> int = <fun>
# prodAdd 1 2;;
- : int = 3
# prodAdd2 1 2;;
- : int = 3
# prodAdd 1;;
- : int -> int = <fun>
# prodAdd2 1;;
- : int -> int = <fun>
> Now I want to do a function that takes a ref to a list and returns a
> function that adds items to the list and produce a function that
> returns another that returns the list. How do I do that?
>
> let prod_list_acc a =
> fun x -> a := x :: !a; true;;
>
> let return_acc a =
> fun () -> !a;;
>
> but that gives a "unit -> int list" =. How do you get a copy of the
> list values?
>
>
> This might seem like a crazy thing to do but I am toying with an idea
> relating to a paper I read on traits. Instead of having classes at
> all you can just have traits, closures and mutable values.
That's not a very functional style. It does seem to work for me with
the following syntax, though:
# let list_acc a x = a := x :: !a; ();;
val list_acc : 'a list ref -> 'a -> unit = <fun>
# let return_list a = !a;;
val return_list : 'a ref -> 'a = <fun>
# return_list a;;
- : int list = [1; 2; 3; 4; 5]
# list_acc a 6;;
- : unit = ()
# return_list a;;
- : int list = [6; 1; 2; 3; 4; 5]
--
Dustin Sallings
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next prev parent reply other threads:[~2003-11-17 21:02 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-11-17 19:37 chris.danx
2003-11-17 21:02 ` Dustin Sallings [this message]
2003-11-17 21:48 ` Dustin Sallings
2003-11-17 21:43 ` Brian Hurt
2003-11-17 21:35 ` chris.danx
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