[racket-dev] Announcing Soft Contract Verification tool

On Jan 15, 2015, at 11:13 AM, David Van Horn <dvanhorn at cs.umd.edu> wrote:

> On 1/15/15, 11:04 AM, Matthias Felleisen wrote:
>> 
>> Well that got me all excited. So I tried to get the sample module
>> to pass the verification step -- until I realized how restricted
>> the grammar is!
>> 
>> (module f racket (provide (contract-out [f (real? . -> .
>> integer?)])) (define (f n) (/ 1 (- 100 n))))
>> 
>> I would love to be able to use at least (and/c real? (>/c 0)) for
>> the domain so I can get the example done.
>> 
>> Or am I overlooking a way to make this work here?
> 
> The >/c contract is there, but missing from the grammar (we'll fix that).
> 
> But (>/c 0) will not make this program verify.  You want this contract:
> 
> ((and/c real? (lambda (x) (not (= x 100)))) . -> . real?)
> 
> Using this contract, the program verifies.


My contract is stronger than yours. So why will it not go through?