# Code doesn't work, not surprised however it's yet another example from a book **URL:** \ **Category:** Questions & Answers\ **Created:** [February 16, 2025, 5:00am UTC](https://racket.discourse.group/t/code-doesnt-work-not-surprised-however-its-yet-another-example-from-a-book/3568 "2025-02-16T05:00:02Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![munroec](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@munroec](https://racket.discourse.group/u/munroec)\ **Post date:** [February 16, 2025, 5:00am UTC](https://racket.discourse.group/t/code-doesnt-work-not-surprised-however-its-yet-another-example-from-a-book/3568/1 "2025-02-16T05:00:02Z")
Things were was executing ok until I added section that I have marked which was supposed to plot the the set union. I was very suspicious of the code that as the offending terms were never defined. Any thoughts on what it should be? And a general question, what is the significance when some identifiers are all in capitol letters, other than the obvious of differentiating it from, a keyword of same name. Is there something more too that? I know it's a lo of questions however, I've searched through the online docs a my small library of books on Racket. Too either the answers are in there or I've finally slipped over the edge and ready to. be moved to Shady Pines Elder Estate! 🤣 Cheers, Munroe The Code: ```scheme #lang racket ;set theory 2 PTFW pp 97 thru top of pp 100 (require racket/draw) (define WIDTH 150) (define HEIGHT 100) (define venn (make-bitmap WIDTH HEIGHT)) (define dc (new bitmap-dc% [bitmap venn])) (send dc scale 1.0 -1.0) (send dc translate (/ WIDTH 2) (/ HEIGHT -2)) (send dc set-smoothing 'smoothed) (send dc set-pen "black" 2 'solid) (define IN-BRUSH (new brush% [color "green"])) (define OUT-BRUSH (new brush% [color (make-object color% 220 220 220)])) (define (rect x y w h b) (let ([x (- x (/ w 2))] [y (- y (/ h 2))]) (send dc set-brush b) (send dc draw-rectangle x y w h))) (define (circle x y r b) (let ([x (- x r)] [y (- y r)]) (send dc set-brush b) (send dc draw-ellipse x y (* 2 r) (* 2 r)))) (define (universe b) (rect 0 0 (- WIDTH 10) (- HEIGHT 10) b)) (universe OUT-BRUSH) (circle 0 0 30 IN-BRUSH) venn (send dc erase) (universe IN-BRUSH) (circle 0 0 30 OUT-BRUSH) venn (define (piscis x y r b) (let* ([y (- y r)] [2r (* 2 r)] [y1 (sqrt (- (sqr r) (sqr x)))] ;y-intercept [π pi] [ø (asin (/ y1 r))] [𝜭 (- π ø)] [path (new dc-path%)]) (send dc set-brush b) (send path move-to 0 (- y1)) (send path arc (- x r) y 2r 2r 𝜭 (+ π ø)) (send path arc (- (- x) r) y 2r 2r (- ø) ø) (send dc draw-path path))) (define SET-BRUSH (new brush% [color (make-object color% 220 255 250)])) (define(venn-bin b1 b2 b3) (universe OUT-BRUSH) ;Racket obviously complains that "CIRCLE-OFF is an unbound entity. I ;considering typos such as the offending term should be lower case. But more ;troubling I have no clue what that general form is trying to accomplish? ***** (circle (- CIRCLE-OFF) 0 30 b1) ***** (circle CIRCLE-OFF 0 30 b3) ***** (piscis CIRCLE-OFF 0 30 b2) (print venn)) (venn-bin IN-BRUSH IN-BRUSH IN-BRUSH) ``` ---
**Author:** ![rogert](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/rogert/32/2474_2.png) [@rogert](https://racket.discourse.group/u/rogert)\ **Post date:** [February 16, 2025, 7:07am UTC](https://racket.discourse.group/t/code-doesnt-work-not-surprised-however-its-yet-another-example-from-a-book/3568/2 "2025-02-16T07:07:59Z")
Add `(define CIRCLE-OFF 20)` to the code. (Uppercase identifiers are conventionally used as names for constants) ---
**Author:** ![damien\_mattei](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/damien_mattei/32/2706_2.png) [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Post date:** [February 16, 2025, 10:20am UTC](https://racket.discourse.group/t/code-doesnt-work-not-surprised-however-its-yet-another-example-from-a-book/3568/3 "2025-02-16T10:20:48Z")
For those wanting to learn Scheme/Racket from scratch here is a cool course: > **[Intro Scheme en L1 Info et Math](http://jean.paul.roy.free.fr/PCPS/PF1/scheme1.html)** > > Scheme Racket unfortunately in "Français" only 😅 ---
**Author:** ![munroec](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@munroec](https://racket.discourse.group/u/munroec)\ **Post date:** [February 16, 2025, 1:58pm UTC](https://racket.discourse.group/t/code-doesnt-work-not-surprised-however-its-yet-another-example-from-a-book/3568/4 "2025-02-16T13:58:29Z")
Hi Rodger, Thank you for the very prompt reply to my newbie question. Well that certainly fixed the problem however, why? I understand defining CIRCLE-OFF but why "20” ?? As an aside, I’m constantly frustrated by the errors and/or omissions in all of the texts on Racket currently in my library. I would dearly love to purchase a tutorial text that wasn’t plagued with issues like, this and whilst I’m whining , most of them lack an index so the inclusion of that would be a huge plus. Cheers, M.C. “Moe” Clayton “Old age ain't no place for sissies.” ― Bette Davis Sent from ---
**Author:** ![munroec](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@munroec](https://racket.discourse.group/u/munroec)\ **Post date:** [February 16, 2025, 2:02pm UTC](https://racket.discourse.group/t/code-doesnt-work-not-surprised-however-its-yet-another-example-from-a-book/3568/5 "2025-02-16T14:02:35Z")
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**Author:** ![munroec](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@munroec](https://racket.discourse.group/u/munroec)\ **Post date:** [February 16, 2025, 3:08pm UTC](https://racket.discourse.group/t/code-doesnt-work-not-surprised-however-its-yet-another-example-from-a-book/3568/6 "2025-02-16T15:08:17Z")
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