[plt-scheme] Describe Function

Oh, there is an unsafe-vector-set! - and unsafe-struct-ref and set!.

On Tue, Nov 10, 2009 at 4:51 PM, Doug Williams <m.douglas.williams at gmail.com
> wrote:

> 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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