[racket-dev] Announcing Soft Contract Verification tool

On 1/15/15, 11:17 AM, Matthias Felleisen wrote:
> 
> 
> 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?
> 
> 

100 is (>/c 0) but (f 100) divides by zero.

David