Those who look shall be rewarded:
(define unsafe-factorial
(invariant-assertion
(-> (and/c integer? (>=/c 0)) (and/c integer? (>=/c 0)))
(lambda (n)
(if (zero? n)
1
(* n (unsafe-factorial (- n 10)))))))
(unsafe-factorial 5)
BUT @robby
the invariant-assertion uses the contract region machinery (or something like
your syntax rule) and thus blames the (seemingly) wrong party:
> unsafe-factorial: contract violation
> expected: (and/c real? (not/c negative?))
> given: -5
> in: an and/c case of
> the 1st argument of
> (->
> (and/c
> integer?
> (and/c real? (not/c negative?)))
> (and/c
> integer?
> (and/c real? (not/c negative?))))
> contract from: anonymous-module
> blaming: anonymous-module
> (assuming the contract is correct)
> at: unsaved-editor:21.3
> On May 6, 2017, at 6:27 PM, Daniel Prager <daniel.a.pra...@gmail.com> wrote:
>
> Thanks Georges
>
> It looks suggestive, but I'm struggling to follow the details of
> with-contract / blame-id. An example of use would be very helpful in the docs!
>
> Have you used this construct?
>
>
> Dan
>
>
> On Sun, May 7, 2017 at 7:44 AM, Dupéron Georges <jahvascriptman...@gmail.com
> <mailto:jahvascriptman...@gmail.com>> wrote:
> Le samedi 6 mai 2017 23:38:29 UTC+2, Daniel Prager a écrit :
> > Although I understand why my macro does this
> >
> > unsafe-factorial: contract violation
> > ...
> > blaming: (function fn/impl)
> > ...
> > at: unsaved-editor:13.15
> >
> >
> > Ideally I would prefer one which blames unsafe-factorial
> >
> > unsafe-factorial: contract violation
> > ...
> > blaming: (function unsafe-factorial)
> > ...
> > at: unsaved-editor:13.15
> >
> >
> > i.e. it's leaking an auxillary introduced by the macro (fn/impl) into the
> > message & Dr Racket. It seems that the line-number refers to the line that
> > defines unsafe-factorial, though, which looks right.
>
> Perhaps with-contract's `blame-id` can help?
>
> http://docs.racket-lang.org/reference/attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._with-contract%29%29
>
> <http://docs.racket-lang.org/reference/attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._with-contract%29%29>
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