[racket-dev] [plt] Push #27395: master branch updated

On Fri, Aug 30, 2013 at 8:40 PM, Eric Dobson <eric.n.dobson at gmail.com> wrote:
> As it stands the Set type constructor is for hash sets. Changing that
> would break backwards compatibility and pr13989 is for the issue of
> changing the meaning/any change.
>
> I think there is a bunch of existing code that assumes that Set is
> exactly hashsets, or at least covariant.

I think we, like Racket in general, should probably follow the
slightly more awkward path that Carl ended up on for backwards
compatibility, with `set?` for immutable hash sets, and `generic-set?`
for generic sets, and similarly for the type names.

Sam

>
> On Fri, Aug 30, 2013 at 5:37 PM, Vincent St-Amour <stamourv at ccs.neu.edu> wrote:
>> I was thinking of the `Set' type constructor as meaning generic set,
>> which is why I gave that type to `generic-set?'. This interpretation is
>> a problem because TR treats sets as covariant.
>>
>> If we make sets invariant, could TR support generic sets? [1] Or are
>> there other issues I'm missing?
>>
>> Vincent
>>
>>
>> [1] Better support would also include subtyping between lists and sets.
>>
>>
>> At Fri, 30 Aug 2013 16:38:11 -0700,
>> Eric Dobson wrote:
>>>
>>> Isn't the assymetric check the wrong way? If it returns true, we know
>>> nothing because it might not be a hash-set, but if it returns false
>>> then we know that it is not a hash set?
>>>
>>> On Fri, Aug 30, 2013 at 3:30 PM, Asumu Takikawa <asumu at ccs.neu.edu> wrote:
>>> > On 2013-08-30 16:15:23 -0400, Sam Tobin-Hochstadt wrote:
>>> >> I worry about mutable sets here, but I can't think of any bugs it can
>>> >> cause ATM.
>>> >
>>> > I don't have any segfault-causing bugs, but here's a violation of the blame
>>> > theorem:
>>> >
>>> >   #lang racket
>>> >
>>> >   (module a0 racket
>>> >     (define s (mutable-set 1 2 3))
>>> >     (provide s))
>>> >
>>> >   (module a typed/racket
>>> >     (require/typed (submod ".." a0) [s Any])
>>> >     (: x (Setof Any))
>>> >     (define x (assert s generic-set?))
>>> >     (provide x))
>>> >
>>> >   (require 'a)
>>> >   x
>>> >
>>> > Cheers,
>>> > Asumu
>>> > _________________________
>>> >   Racket Developers list:
>>> >   http://lists.racket-lang.org/dev