Let's make Spencer's question concrete. Say we have this situation:
#lang racket
;; contracts set up boundaries between two regions of a program, say two
modules
;;
---------------------------------------------------------------------------------------------------
;; the library
(module server racket
(provide (contract-out
[struct bezier-control-point ((x (and/c number? (between/c 0 1)))
(y number?))]
[cubic-bezier (-> bezier-control-point?
bezier-control-point?
(->* ((and/c number? (between/c 0 1)))
(#:clamp-range boolean?)
number?))]))
(struct bezier-control-point (x y) #:transparent)
(define (cubic-bezier a b)
;; now produce a curve via Bezier triangulation
(lambda (x #:clamp-range [cr #f])
x)))
;;
---------------------------------------------------------------------------------------------------
;; the module that uses it
(module client racket
(require (submod ".." server))
(define a (bezier-control-point 0.1 5.0))
(define b (bezier-control-point 0.3 9.0))
((cubic-bezier a b)
;; a contract violation because i isn't comparable
(sqrt -1)))
;;
---------------------------------------------------------------------------------------------------
;; run program run
(require 'client)
I assume you want to see other violations. Can you explain with this example
w/o going into Bezier?
(I just know enough about Bezier to draw curves.)
-- Matthias
On Oct 1, 2014, at 10:46 PM, Alexander McLin <alex.mc...@gmail.com> wrote:
> Hello,
>
> I've been working on a sample project to better understand how to use the
> contract system. I created a simple Bezier curve implementation and am using
> (provide (contract-out...) to attach contracts to the provided bindings.
>
> Basically I have a procedure called cubic-bezier that accepts two control
> point structs used to define the curve. It returns another procedure that
> actually generates the curve, it accepts an integer parameter that lies on
> [0, 1] and an optional keyword #:clamp-range. The generator procedure returns
> a number.
>
> The control point structure is a simple posn type that accepts X and Y fields
> where X must be between 0 and 1, and Y is allowed to be any number.
>
> Here are the contracts I defined provisionally:
>
> (provide (contract-out
> [struct bezier-control-point ((x (and/c number? (between/c 0 1)))
> (y number?))]
> [cubic-bezier (-> bezier-control-point?
> bezier-control-point?
> (->* ((and/c number? (between/c 0 1)))
> (#:clamp-range boolean?)
> number?))]))
>
> For the contract attached to cubic-bezier using ->, my thinking was to use
> ->* to generate the contract for the procedure returned by cubic-bezier but
> it's not working, meaning I'm not getting the any contract violations I'm
> expecting when giving bad inputs to cubic-bezier's value.
>
> How can I attach a more complex contract to cubic-bezier's value?
>
> Thank you
> Alexander McLin
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