Actually I wasn't quite ready to move on. When I apply (curve 3) where (define curve (cubic-bezier a b) a and b are bezier-control-point?
I get the following contract error: --------------------------------------------------------------------------- *(curve 3)* *. . cubic-bezier: contract violation* * expected: (and/c number? (between/c 0 1))* * given: 3* * which isn't: (between/c 0 1)* * in: the 1st argument of* * the range of* * (->* * bezier-control-point?* * bezier-control-point?* * (->** * ((and/c number? (between/c 0 1)))* * (#:clamp-range boolean?)* * number?))* * contract from: * * /home/alexander/Workspace/Racket/cubic-bezier.rkt* * blaming: /home/alexander/Workspace/Racket/experimental.rkt* * at: /home/alexander/Workspace/Racket/cubic-bezier.rkt:8.11* ---------------------------------------------------------------------------- Is there a way I can fine-tune the error message so instead of saying * in: the 1st argument of* * the range of* * (->* * bezier-control-point?* * bezier-control-point?* * (->** * ((and/c number? (between/c 0 1)))* * (#:clamp-range boolean?)* * number?))* It says * in: the 1st argument of* * the range of* * (->** * ((and/c number? (between/c 0 1)))* * (#:clamp-range boolean?)* * number?)* The above contract is really what is coming into play here when using curve, the surrounding -> form is a distraction and I stare at it for a few moments mentally parsing to find the right part that is being violated. The -> contract is only relevant to cubic-bezier and I think confusing because the lambda that is returned from cubic-bezier may be called after some time has passed and — at least for me — cubic-bezier is long since gone, and thus out of mind. Alexander McLin On Fri, Oct 3, 2014 at 9:59 PM, Alexander McLin <alex.mc...@gmail.com> wrote: > Good evening Mathias, > > After studying your program and mine, and running various permutations, I > understand where I was going wrong. It appears that while doing manual > experimentation I had gotten confused to which module I was actually in the > REPL when calling various functions by hand. Also my test cases weren't > fine grained enough to detect each unique contract violation generated by > suitable bad inputs. > > Thanks Mathias! Your examples have helped to sharpen my understanding of > how contract boundaries work. > > Alex > > On Thu, Oct 2, 2014 at 2:36 PM, Matthias Felleisen <matth...@ccs.neu.edu> > wrote: > >> >> If you use this as the program: >> >> #lang racket >> >> ;; contracts set up boundaries between two regions of a program, say two >> modules >> >> ;; >> --------------------------------------------------------------------------------------------------- >> ;; the library >> (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+ test >> (require (submod "..")) >> >> (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))) >> >> >> drracket or raco test file.rkt will show contract errors. >> >> >> >> >> On Oct 2, 2014, at 1:50 PM, Alexander McLin <alex.mc...@gmail.com> wrote: >> >> > Spencer, I'm calling cubic-bezier from within a (module+ test (require >> submod "..")...) form that itself is defined in the file where cubic-bezier >> is defined. Also I tried from within REPL and requiring the code file. >> > >> > Matthias, >> > >> > I ran your example and it works exactly the way I wanted. The lambda >> returned from cubic-bezier properly raises contract violations when bad >> inputs are given for the required parameter and optional keyword. >> > >> > Examining the differences between your example and my original >> implementation, my functions are directly defined in top level in the file, >> after #lang racket, not wrapped within a module. And I'm running my test >> cases within a (module+ test (require submod "..")) form. >> > >> > In my test cases within (module+ test...), violations are correctly >> reported when I give bad inputs to cubic-bezier and bezier-control-point >> structs. Except the lambda, no violations are reported with bad inputs. Is >> it because I'm incorrectly using modules? I had thought that module+ and >> (require submod "..") would allow the contract system to come into full >> force. >> > >> > >> > >> > On Thu, Oct 2, 2014 at 9:20 AM, Matthias Felleisen < >> matth...@ccs.neu.edu> wrote: >> > >> > 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 >> > > ____________________ >> > > Racket Users list: >> > > http://lists.racket-lang.org/users >> > >> > >> >> >
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