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

On Wed, Jan 22, 2014 at 09:26:09PM -0000, Jon Harrop wrote:
> 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.

So Some x is the value x unless x is an option type? That wouldn't
work for polymorphic functions, those taking 'a option. You can't
encode 'a option differently depending on 'a unless you have a flag
for which encoding it used as well.

I think you can only have one: option types using nil or 'a option
option.

Which doesn't mean you can't have nil too, just not to represent the
None part of 'a option. In ocaml you would need a new type syntax like

type 'a ptr_option = NIL | PTR of 'a constraint type b . 'a != b ptr_option

MfG
	Goswin