> On May 5, 2017, at 11:30 PM, Daniel Prager <daniel.a.pra...@gmail.com> wrote:
>
> Thank-you Matthias
>
> That's neat!
>
> And yes, I can write a basic macro. By introducing #:freevar I was able to
> improve the blame situation, but the abstraction is a bit leaky ...
>
> (define-syntax-rule (define/tight (fn args ...)
> ctc
> body ...)
> (begin
> (define (fn args ...) (fn/impl args ...))
> (define/contract (fn/impl args ...)
> ctc
> #:freevar fn ctc ; Directs blame to "fn/impl" rather than the
> enclosing module
> body ...)))
>
I am not sure what you mean by ‘leaky’. When I run this,
(define/tight [unsafe-factorial n]
(-> (and/c integer? (>=/c 0)) (and/c integer? (>=/c 0)))
(if (zero? n)
1
(* n (unsafe-factorial (- n 10)))))
(unsafe-factorial 5) ; Does not terminate
I get
> 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: (function fn/impl)
> (assuming the contract is correct)
> at: unsaved-editor:13.15
The only thing that leaks is that >/c is actually an and/c contract — and I
will say I am rather surprised by that.
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