Re: [Caml-list] kprintf with user formatters

[Markus Mottl <markus@oefai.at>]

On Fri, 16 Jul 2004, Pierre Weis wrote:
> No, this is not safe: you break the type system and create buggy
> values like that.

True, but unit values are not very useful so if the user ignores them
(as usual), there won't be any problems.

> # let log b fmt = 
>     if b then Printf.printf fmt else 
>     let rec f x = Obj.magic f in f fmt;;
> val log : bool -> ('a, out_channel, unit) format -> 'a = <fun>
> # log false "";;
> - : unit = <unknown constructor>
> # let x = log false "";;
> val x : unit = <unknown constructor>
> # Marshal.to_string;;
> - : 'a -> Marshal.extern_flags list -> string = <fun>
> # Marshal.to_string x [];;
> Exception: Invalid_argument "output_value: abstract value (outside
> heap)".
> 
> There is clearly something wrong!

Oh, come on, don't prohibit my use of Obj.magic by demonstrating strange
interactions with the equally unsafe Marshal-module ;-)

Btw., what has happened to generics?  They were said to solve problems
associated with type safety and I/O.  Any intentions to put them into
the experimental CVS-tree of OCaml?

Regards,
Markus

-- 
Markus Mottl          http://www.oefai.at/~markus          markus@oefai.at

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