> On May 7, 2017, at 1:26 AM, Daniel Prager <daniel.a.pra...@gmail.com> wrote:
>
> Putting this new set-up through its paces I think I've found a few issues:
>
> 1. Default argument goes missing from post-condition, leading to an
> unexpected error …
(define (default-y x) 0)
(define/contract (greater-than-square? x [y (default-y x)])
(->i ([x real?])
([y real?])
[result boolean?]
#:post (x y result)
(equal? result (< (sqr (if (unsupplied-arg? y) (default-y x) y)) x)))
(> x (sqr y)))
(greater-than-square? 10)
> 3. post-conditions appear to be called twice ...
>
> Is there a double boundary crossing on post-conditions?
Yes! Your syntax rule says to check the post-condition twice:
(define-syntax-rule (define/tight (fn args ...)
ctc
body ...)
(begin
(define (fn args ...) (fn/impl args ...))
(with-contract fn
([fn/impl ctc])
; #:freevar fn ctc ;;;; **** now you see it checked only
once
(define (fn/impl args ...)
body ...))))
> Finally, some timings.
Measure with outer contract and remove the inner define/tight. If you wrote
this algorithm with a loop in Eiffel, instead of a tail-recursive function, you
wouldn’t check the invariant for every loop iteration either
— Matthias
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