[racket] Structs and syntax-local-value ... how is the struct name overloaded?

But I don't see how the same binding can be a transformer and also return
something else (like a list, or a checked-struct-info-thing) via
syntax-local-value.

If I bind my-fn as a transformer, then any other macros that use it with
syntax-local-value will receive the transformer procedure back, not any
special meta data.  And if I bind it as meta data directly, ie
(define-syntax my-fn 'something) then it works with syntax-local-value but
any attempts to use it as a transformer result in illegal syntax.

Even if I create a transformer that returns a struct which implements both
prop:procedure and prop:struct-info, using that binding with
syntax-local-value will return the transformer procedure itself, rather
than the final struct.



On Sun, Jan 19, 2014 at 8:04 PM, Carl Eastlund <carl.eastlund at gmail.com>wrote:

> Yes, I believe that the name of a structure defined by "struct" is bound
> at syntax-time to a value that implements both prop:procedure, so that it
> can expand to a use of the constructor when used in an expression, and
> prop:struct-info so that it can be use to look up static information when
> passed to relevant macros.
>
> Carl Eastlund
>
>
> On Sun, Jan 19, 2014 at 11:00 PM, Scott Klarenbach <scott at pointyhat.ca>wrote:
>
>> How is it that the definition of (struct my-name (x y)) can bind
>> *my-name* both as a #<procedure:my-name> at runtime and a
>> transformer-binding *my-name* that at compile time (via
>> syntax-local-value) produces #<procedure:self-ctor-checked-struct-info>.?
>>
>> Or, put another way, how can I define a transformer *my-fn* that
>> produces syntax, but that also exposes hidden meta-data under the same
>> binding to other macros that might wish to know about the binding at
>> compile time?
>>
>> I'm specifically wondering how the overloading works.  Is it some clever
>> use of prop:procedure?
>>
>> Thanks.
>>
>> --
>> Talk to you soon,
>>
>> Scott Klarenbach
>>
>> PointyHat Software Corp.
>> www.pointyhat.ca
>> p 604-568-4280
>> e scott at pointyhat.ca
>> 200-1575 W. Georgia
>> Vancouver, BC V6G2V3
>>
>> _______________________________________
>> To iterate is human; to recur, divine
>>
>> ____________________
>>   Racket Users list:
>>   http://lists.racket-lang.org/users
>>
>>
>


-- 
Talk to you soon,

Scott Klarenbach

PointyHat Software Corp.
www.pointyhat.ca
p 604-568-4280
e scott at pointyhat.ca
200-1575 W. Georgia
Vancouver, BC V6G2V3

_______________________________________
To iterate is human; to recur, divine
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20140119/dbb0ffc0/attachment.html>