Re: [Caml-list] Changing precedence and placement of attributes

[Maxence Guesdon <Maxence.Guesdon@inria.fr>]

On Mon, 09 Mar 2015 14:37:17 +0100
Alain Frisch <alain.frisch@lexifi.com> wrote:

> On 03/09/2015 02:16 PM, Maxence Guesdon wrote:
> > I'm quite "shocked" as it becomes inconsistent with other precedences
> > in type definitions. By now
> >    int * int list
> > is parsed as
> >    int * (int list)
> > and not as
> >    (int * int) list
> >
> > I would expect attributes to be associated the same way.
> 
> Attributes really don't behave as type constructors; for instance,
> 
>     (int, int) [@foo]
> 
> is not allowed in type expressions.

Of course.

> I'd be more concerned about how attributes behave across various 
> syntactic categories for similarly looking fragments.  For instance, in 
> expressions
> 
>    x * y [@foo]
> 
> is already currently parsed as
> 
>    (x * y) [@foo]
> 
> 
> But
>   - "x, y [@foo]" is parsed as "x, (y [@foo])"
>   - "x * y [@foo] * z" is accepted as an expression, and parsed as "(x * 
> y)[@foo] * z".

This looks more intuitive/natural to me and more consistent with the
rest of the language.

I'm thinking about newcomers, when I'll have to explain them that rather
than writing "int * int list", they'll need parentheses in "(int * int)
list" to talk about list of pairs, but when it comes to attributes it's
the contrary. Sure, the language was not complicated enough :) Even if
attributes are not type constructors, one would expect some consistent
"feeling".

> > How would be parsed the following:
> >    int * int [@foo] * int
> > ?
> 
> This would be rejected.  Doing the same as for expression would be 
> weird, since * is a n-ary construction in types, not a binary operator.

If I understand, you mean that
  type t = int * int [@foo] * int
would be rejected and we use instead:
  type t = int * (int [@foo]) * int

Again, it's really not natural to me.
- m

> (Note: Jérémie prepared a nice table in his pull request 152 on Github; 
> it shows how various forms are interpreted currently and after the change.)
> 
> 
> Alain