[racket-dev] struct contracts

My answers are:

1. There isn't, but I've been planning to do this as soon as I revisit define-struct/contract in the new chaperone/impersonator world.

2. It's doable, but hasn't been done yet.  I'll try and keep this in mind when I revisit the things listed in 1.  If I were to do it, I'd imagine it'd look something like:

(define-struct/contract foo ([bar number?] [moo (bar) <contract using bar>]) #:mutable)

(i.e. it'd use the ->i convention for listing other fields on which this one is dependent.)

Stevie

On Jan 7, 2011, at 12:16 PM, Robby Findler wrote:

> I think that chaperones let us implement this contract, but I don't
> think that you can actually do it yet in the contract library (because
> of the dependency), but Stevie would know best.
> 
> Robby
> 
> On Fri, Jan 7, 2011 at 9:58 AM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
>> 
>> 1. Is there a struct/contract?
>> 
>> 2. I would like to write something like this:
>> 
>> (define-struct/contract foo ([bar number?][moo (->i (*bar*) ([x (and/c number? (>/c bar))]) (r number?))]) #:mutable)
>> 
>> The *bar* is a 'reference' to the bar field, that is, I want to have a function contract for a structure field that depends on the (current) value of a (mutable) field of the same structure.
>> 
>> Is this doable?
>> 
>> 2a. I considered writing a function foo-init that mimics this, but I can't write this either.
>> 
>> Q: Is my only choice to write a class with a contract?
>> 
>> 
>> -- Matthias
>> 
>>