[racket] Is this a bug in contracts?

On Jan 16, 2013, at 7:39 PM, Harry Spier wrote:

> On Mon, Jan 14, 2013 at 9:27 AM, Matthias Felleisen
> <matthias at ccs.neu.edu> wrote:
>> 
>> And Harry, do define certain contracts separately, e.g.,
>> 
>> (define shish/c (is-a?/c shish-D%))
>> 
> 
> If my class has a field of the same class is there a way to do that?
> 
> I.e. both case 1 and case 2 fail on undefined identifier
> Case 1
> #lang racket
> (define pizza-D%/c (is-a?/c pizza-D%))
> 
> (define/contract pizza-D%
>  (class/c [init-field (p pizza-D%/c)])
>  (class pizza-D% (super-new)
>  (init-field p)))
> 
> Case 2
> #lang racket
> (define/contract pizza-D%
>  (class/c [init-field (p pizza-D%/c)])
>  (class pizza-D% (super-new)
>  (init-field p)))
> 
> (define pizza-D%/c (is-a?/c pizza-D%))

First, you mistakenly have the class inherit from itself. You want object% in the super-class position in both cases. 

Second, you don't get to formulate contracts like that. We have flat-rec-contracts but a class contract is a higher-order contract because a class is like a function. 

Contracts and types are incomparable in expressiveness.