[plt-scheme] Describe Function

Instead of the 'everything is a struct' view, you could also use an
'everything is a vector view' and with unsafe-vector-ref take things apart -
even when they are opaque.

(require scheme/unsafe/ops)

(define-struct s (a b c))

(define s1 (make-s 1 3 5))

s1 -> #<s>
(unsafe-vector-ref s1 0) -> #<struct-type:s>
(unsafe-vector-ref s1 1) -> 1
(unsafe-vector-ref s1 2) -> 3
(unsafe-vector-ref s1 3) -> 5

I assume that as long as I stay within the bounds of the underlying
representation (and probably sometimes even if I don't - negative indices
are allowed), unsafe-vector-ref will give gladly me the pieces. At least
there is no unsafe-vector-set!

Doug

On Tue, Nov 10, 2009 at 11:29 AM, Doug Williams <
m.douglas.williams at gmail.com> wrote:

> Sounds good. I was just thinking that a lower level implementation could
> avoid the need to create a vector just to get the variant. But for my code
> it's no big deal.
>
>
> On Tue, Nov 10, 2009 at 11:21 AM, Robby Findler <
> robby at eecs.northwestern.edu> wrote:
>
>> On Tue, Nov 10, 2009 at 12:18 PM, Doug Williams
>> <m.douglas.williams at gmail.com> wrote:
>> > Robby,
>> >
>> > I am going to add your variant procedure to the describe collection.
>>
>> Great!
>>
>> > Are you
>> > happy with the name 'variant' and the contract (-> any/c symbol?)?
>>
>> Yes. (You may want to use substring isntead of regexp-match.)
>>
>> > What is
>> > the relationship between this and object-name?
>>
>> Nothing really. object-name is per-object (and not everything has a name).
>>
>> >  It seems that for actual
>> > structs they return the same value. Would it make sense to change
>> > object-name to return the same value as variant in those cases where it
>> > (i.e., object-name) returns #f? This would trivially make this
>> functionality
>> > available in #lang scheme, which seems to be a good thing.
>>
>> I don't think that that change is really a good idea at this point.
>> Probably would break lots of stuff.
>>
>> Robby
>>
>> > Doug
>> >
>> > On Tue, Nov 10, 2009 at 7:43 AM, Robby Findler <
>> robby at eecs.northwestern.edu>
>> > wrote:
>> >>
>> >> On Tue, Nov 10, 2009 at 8:41 AM, Dave Herman <dherman at ccs.neu.edu>
>> wrote:
>> >> >> This probably doesn't help Doug, but here is another way to define
>> the
>> >> >> function linked above:
>> >> >
>> >> > That's neat, thanks! Has struct->vector always worked on non-structs?
>> >>
>> >> I'm not sure about always, but at some point a while ago, Matthew
>> >> decided that all values are structs (in the sense that you could have
>> >> implemented everything with structs and scope, etc even if some of
>> >> them are implemented in C) and adapted the primitives to make them
>> >> behave accordingly.
>> >>
>> >> Robby
>> >
>> >
>>
>
>
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