Re: [Caml-list] The rec/nonrec debate

[Julien Blond <julien.blond@gmail.com>]

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I agree that making recursitivy more explicit is... well... more explicit
:) But I wonder if, in this case, this is truly relevant. In fact, when I
look at OCaml programs, I see many recursive types and very few type
shadowing. That is, making types non recursive would add some "rec" or
"nonrec" keywords everywhere just to avoid a type alias in a rare case.
From readability point of view, I'm not sure it's a good deal. In the
programs I know, the ratio seems to be something like 70/30 for nonrec/rec
function while, this time, shadowing is quite often used. Here, explicit
"rec" allows us to avoid more "nonrec" elsewhere to continue using
shadowing.



2013/5/20 David House <dhouse@janestreet.com>

> At Jane Street we have a syntax extension that allows one to write
> "type nonrec t = ...".
>
> I too think that non-recursive is the right default. My argument is
> mostly as follows: it's nice to have nonrecursive values be the
> default, because shadowing is so useful. And it's confusing to have
> two different defaults for types and values.
>
> I also agree that we can't change this for ocaml.
>
> On 20 May 2013 15:31, Dario Teixeira <darioteixeira@yahoo.com> wrote:
> > Hi,
> >
> >
> > As you know, there is in OCaml some asymmetry regarding the rec/nonrec
> > defaults for type and value declarations.  Types are recursive by default
> > and there's no way to "unrecurse" them, whereas values are by default not
> > recursive and can be made recursive via the "rec" keyword.
> >
> > The unrecursiveness of type declarations is cause for some chagrin, as a
> > recent ticket on Mantis demonstrates [1].
> >
> > Here's something I wonder: if one were to wipe the slate clean, is there
> > consensus among the community about the best defaults?  I'm leaning
> towards
> > having nonrec as the default behaviour for *both* types and values, and
> > using "rec" as the keyword for recursive types and values.  This scheme
> > would obviate the need for an actual "nonrec" keyword.
> >
> > Obviously, such a change would be too intrusive to make to OCaml.
>  However,
> > since people are working on "Next Generation ML" languages like Mezzo
> [2],
> > I think it would be good to get the community's pulse on this subject.
> > (Btw, from the examples posted on Mezzo's homepage, it seems to use the
> > same defaults as OCaml).
> >
> > Your thoughts?
> >
> > Best regards,
> > Dario Teixeira
> >
> > [1] http://caml.inria.fr/mantis/view.php?id=6016
> > [2] http://gallium.inria.fr/~protzenk/mezzo-lang/
> >
> >
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