On Fri, 2004-07-16 at 03:20, John Prevost wrote:
> On Thu, 15 Jul 2004 10:38:14 -0500 (CDT), Brian Hurt <bhurt@spnz.org> wrote:
> > One of the problems with returning error conditions instead of throwing
> > exceptions is the cost of boxing a 'a option.  I'd like to advocate for
> > the idea of unboxing 'a options.
> 
> This has been discussed before.  The essential problem is this:
> 
> Currently:
> 
> type 'a option is not the same as type 'a option option
> Some Some 1 is not the same as Some 1
> Some None is not the same as None
> 
> With unboxed options:
> 
> type 'a option is the same as type 'a option option
> Some Some 1 is identical to Some 1
> Some None is identical to None

This is wrong. The representation being suggested is:

None -> NULL
Some 'a -> pointer to 'a

Clearly this represntation is faithful and nothing
more than an interpretation of the corresponding C 
concept.

Some Some 1 is obviously distinct from Some 1 as reqiuired:
pointer to pointer to 1 is distinct from pointer to 1.
Some None is a pointer to NULL, which is distinct from 
None which is just NULL.

Perhaps this won't work with the Ocaml runtime but
there is no problem with the typing.

-- 
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net



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