Re: fancy types (was Re: [Caml-list] ocaml killer)

[William Lovas <wlovas@stwing.upenn.edu>]

On Fri, Jan 30, 2004 at 11:36:13AM +0100, Thomas Fischbacher wrote:
> 
> On Thu, 29 Jan 2004, William Lovas wrote:
> 
> >     # type ('a, 'b) specialist = S of (('a, 'b) specialist -> 'a -> 'b);;
> >     type ('a, 'b) specialist = S of (('a, 'b) specialist -> 'a -> 'b)
> >     # let fac n =
> >         let do_rec (S specialist) n =
> >           if n = 0 then
> >             1
> >           else
> >             n * specialist (S specialist) n
> >         in
> >         do_rec (S do_rec) n;;
> >     val fac : int -> int = <fun>
> 
> Hm, correct me if I am wrong, but to me this looks as if you had to 
> unnecessarily cons at every recursive call...

Well, it depends on what you mean by "unnecessarily" and what you mean by
"cons".  First, if by "cons" you mean "call a constructor", then yes, i did
have to cons at every recursive call.  However, if by "cons" you mean
"allocate memory", i can't say for sure by looking at this code -- it says
nothing about the optimizations applied to variant types during compilation
or potential opportunities for structure sharing.  I strongly suspect that
memory need not be allocated, though, in which case the answer is no, i did
not have to allocate memory at every recursive cell.

As far as "unnecessarily" goes, to me the calls are perfectly necessary --
otherwise the code wouldn't make sense -- I think in types first and code
second. :)

So if efficiency is your concern, you've nothing to worry about.  If its
verbosity, then you have a fair argument -- you just have to weigh the
development time benefits against the small amount of extra code you have
to write beyond what LISP would require you to write.  Personally, i think
it's worth it, but that's just an opinion.

cheers,
William

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