[racket] struct-copy with sub-types

Hi, and sorry for the delay. I've pushed a fix for this, altho it is
more like a new feature since the code below still doesn't work--- you
have to explicitly name the struct that had the field when it isn't
the first argument to struct-copy.

Robby

On Fri, Mar 25, 2011 at 7:52 AM, Pierpaolo Bernardi <olopierpa at gmail.com> wrote:
> On Wed, Mar 23, 2011 at 00:49, Nadeem Abdul Hamid <nadeem at acm.org> wrote:
>> Is there anything like struct-copy that works to functionally update a
>> field value in a structure, where the field happens to be defined in
>> the super-type? In the example below, I want to "functionally update"
>> a field of the sub structure inherited from the base definition...
>>
>>
>> (struct base (a b) #:transparent)
>> (struct sub base (c) #:transparent)
>>
>> (define S (sub 1 2 3))
>>
>> (struct-copy sub S [c 4]) ; works
>> ; doesn't work: (struct-copy sub S [b 4])
>> (struct-copy base S [b 4]) ; produces a base, not sub
>
> No answers?
>
> it looks to me that
>
> (struct-copy sub S [b 4])
>
> should work, but it doesn't.  Isn't this a bug?
>
> If it is not considered a bug, maybe the docs need a clarification?
>
> Cheers
> P.
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