RE: [Caml-list] How much optimized is the 'a option type ?

["Jon Harrop" <jon@ffconsultancy.com>]

Goswin wrote:
> In F#, with nil pointer, that will be a problem. But I guess nobody ever
has 'a option option types there

I believe the representation of Some None in F# is a heap allocated block
containing a NULL pointer.

Cheers,
Jon.

-----Original Message-----
From: caml-list-request@inria.fr [mailto:caml-list-request@inria.fr] On
Behalf Of Goswin von Brederlow
Sent: 20 January 2014 10:17
To: caml-list@inria.fr
Subject: Re: [Caml-list] How much optimized is the 'a option type ?

On Fri, Jan 17, 2014 at 12:23:32PM +0100, Jonathan Kimmitt wrote:
> In my humble opinion the main purpose of Some _ | None is to avoid the 
> requirement for a nil pointer in OCaml. If an external function wants 
> to return nil in order to indicate, for example that a certain 
> resource is not available, it can return None instead and this 
> prevents dereferencing a nil pointer in OCaml because the None cannot 
> be dereferenced. If you compare this behaviour with the inferior clone 
> F# written by Microsoft, you can see that one of the things they added 
> to the language was a nil pointer, thus abandoning all type safety 
> immediately and all because they did not want to change their .NET 
> runtime system for C# etc. They also have the notion of initialising a 
> typed object to in an invalid default, which is another obvious 
> disaster area. Oh and did I mention operators like +/- etc are overloaded
so you cannot infer function types without adding type annotations.
> The final insult is to make indentation significant in the syntax so 
> that if you post a program to a list which does not respect whitespace 
> (for example using a well-known Microsoft mail client), it completely 
> destroys the meaning of the program.
> 
> I'm sure the authors of F# have their reasons for making all these 
> changes, and I'm not one to stand in the way of progress, and I don't 
> set out to offend anybody, but I think they got it wrong ...

You could use the following representaion for 'a option:

None -> NULL pointer
Some x -> value x (meaning pointer for complex types, tagged integer eles)

This looks fine at first and typesafe. A pointer can never be NULL, same for
a tagged integer. BUT

None -> NULL
Some None -> NULL
Some Some x -> value x

You could no longer have 'a option option types. In F#, with nil pointer,
that will be a problem. But I guess nobody ever has 'a option option types
there.

MfG
	Goswin

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