# Latest **URL:** https://racket.discourse.group/latest.md?page=61 [Latest](https://racket.discourse.group/latest.md) · [Categories](https://racket.discourse.group/categories.md) · [Tags](https://racket.discourse.group/tags.md) **Page:** 62 --- ## [Overscroll in DrRacket](https://racket.discourse.group/t/overscroll-in-drracket/914)
**Author:** [@jbclements](https://racket.discourse.group/u/jbclements)\ **Replies:** 3\ **Last updated:** [April 22, 2022, 5:38pm UTC](https://racket.discourse.group/t/overscroll-in-drracket/914 "2022-04-22T17:38:52Z")
One of my students showed me "overscroll" in VSCode recently, and it seems like a nice feature. Specifically, it allows you to scroll an editor window down until the bottom line of the buffer is about halfway up the scre… --- ## [Racket Mode: user breakpoints with conditions and actions](https://racket.discourse.group/t/racket-mode-user-breakpoints-with-conditions-and-actions/911)
**Author:** [@greghendershott](https://racket.discourse.group/u/greghendershott)\ **Replies:** 0\ **Last updated:** [April 21, 2022, 6:44pm UTC](https://racket.discourse.group/t/racket-mode-user-breakpoints-with-conditions-and-actions/911 "2022-04-21T18:44:34Z")
Just a heads up that I merged an enhancement to the step debugger in Racket Mode. Previously you had a "run to here" command, which you could think of as one, temporary, unconditional breakpoint at a time. Now you can … --- ## [Predicate non-cyclic-pair?](https://racket.discourse.group/t/predicate-non-cyclic-pair/893)
**Author:** [@joskoot](https://racket.discourse.group/u/joskoot)\ **Replies:** 16\ **Last updated:** [April 21, 2022, 10:20am UTC](https://racket.discourse.group/t/predicate-non-cyclic-pair/893 "2022-04-21T10:20:33Z")
Giving a pair with cycles to a procedure that recurs on the car and the cdr of the pair gives problems if the procedure does not check against cycles. I found no predicate for lists without cycles. Predicate list? of rac… --- ## [A Racket Playground](https://racket.discourse.group/t/a-racket-playground/902)
**Author:** [@tvilot](https://racket.discourse.group/u/tvilot)\ **Replies:** 3\ **Last updated:** [April 20, 2022, 4:24pm UTC](https://racket.discourse.group/t/a-racket-playground/902 "2022-04-20T16:24:56Z")
One thing I like about Go is the Go Playground and the Tour of Go. Is there something similar for Racket? Obviously, I can use the REPL or DrRacket and that's fine. But what I would love is a site where I can play with e… --- ## [Does anyone know a way to check a struct instance value and update it?](https://racket.discourse.group/t/does-anyone-know-a-way-to-check-a-struct-instance-value-and-update-it/899)
**Author:** [@codinggeek46](https://racket.discourse.group/u/codinggeek46)\ **Replies:** 3\ **Last updated:** [April 20, 2022, 3:33pm UTC](https://racket.discourse.group/t/does-anyone-know-a-way-to-check-a-struct-instance-value-and-update-it/899 "2022-04-20T15:33:15Z")
I am trying to write a function that computes the price needed for a flight upgrade and updates the points collected. The function takes as argument a holidaymaker struct instance, and if the upgrade field is true, add… --- ## [Help: Where to find ffi/examples](https://racket.discourse.group/t/help-where-to-find-ffi-examples/896)
**Author:** [@rockn](https://racket.discourse.group/u/rockn)\ **Replies:** 3\ **Last updated:** [April 20, 2022, 1:57am UTC](https://racket.discourse.group/t/help-where-to-find-ffi-examples/896 "2022-04-20T01:57:34Z")
Hi, I am learning racket FFI. I want to see more examples. Can someone tell me where to find ffi/examples mentioned in the FFI doc? --- ## [How can i return the max price value of a struct list?](https://racket.discourse.group/t/how-can-i-return-the-max-price-value-of-a-struct-list/891)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 4\ **Last updated:** [April 18, 2022, 1:24pm UTC](https://racket.discourse.group/t/how-can-i-return-the-max-price-value-of-a-struct-list/891 "2022-04-18T13:24:19Z")
i am trying to write an expression which is supposed to return the highest price of a menu list.. as you can see below i have defined a struct and built a menu as a list of menues.it should return 6 becuase thats the mo… --- ## [Extracting lines from big file](https://racket.discourse.group/t/extracting-lines-from-big-file/888)
**Author:** [@jkleiser](https://racket.discourse.group/u/jkleiser)\ **Replies:** 4\ **Last updated:** [April 18, 2022, 9:53am UTC](https://racket.discourse.group/t/extracting-lines-from-big-file/888 "2022-04-18T09:53:09Z")
Hi. I want to extract and/or process certain lines from a rather big file (330 MB, 6.5 million lines). The condition for which lines to handle is based on whether a certain part of the line read is found in a hash set of… --- ## [Which class can i use instead of label to show list and how can order DrRacket to close the previous window after the next one opens?](https://racket.discourse.group/t/which-class-can-i-use-instead-of-label-to-show-list-and-how-can-order-drracket-to-close-the-previous-window-after-the-next-one-opens/890)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 1\ **Last updated:** [April 17, 2022, 4:24pm UTC](https://racket.discourse.group/t/which-class-can-i-use-instead-of-label-to-show-list-and-how-can-order-drracket-to-close-the-previous-window-after-the-next-one-opens/890 "2022-04-17T16:24:08Z")
Hi,i am in the midst of creating a graphical user interface of a story i created,i have this long script ,which is why i stored in a list,so i dont have to paste a long script into the function.I tried to call the list i… --- ## [Is it possible to use Template Variables in constants definitions?](https://racket.discourse.group/t/is-it-possible-to-use-template-variables-in-constants-definitions/885)
**Author:** [@jgomo3](https://racket.discourse.group/u/jgomo3)\ **Replies:** 3\ **Last updated:** [April 15, 2022, 2:04pm UTC](https://racket.discourse.group/t/is-it-possible-to-use-template-variables-in-constants-definitions/885 "2022-04-15T14:04:12Z")
Language: BSL Doc: Template variables A function definition, like (define (f x) ...) has no problem with template variables. But a constant definition, like (define X ...) has problems with template variables, specifi… --- ## [New build system pushed to Git repo](https://racket.discourse.group/t/new-build-system-pushed-to-git-repo/873)
**Author:** [@mflatt](https://racket.discourse.group/u/mflatt)\ **Replies:** 2\ **Last updated:** [April 14, 2022, 9:25pm UTC](https://racket.discourse.group/t/new-build-system-pushed-to-git-repo/873 "2022-04-14T21:25:33Z")
For anyone who builds from source from a Git checkout, beware that the build system has changed. Ideally, you won't notice any difference, but there are bound to be some problems in the next few days and weeks. The chan… --- ## [How can i apply count function to render spec](https://racket.discourse.group/t/how-can-i-apply-count-function-to-render-spec/867)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 1\ **Last updated:** [April 13, 2022, 3:04pm UTC](https://racket.discourse.group/t/how-can-i-apply-count-function-to-render-spec/867 "2022-04-13T15:04:12Z")
Hello i was having difficulty using the function which i created which is supposed to display the number of guesses the program takes to find the players number.i have defined this function not sure if its correct , (d… --- ## [Don't export n-\>th?](https://racket.discourse.group/t/dont-export-n-th/861)
**Author:** [@sorawee](https://racket.discourse.group/u/sorawee)\ **Replies:** 5\ **Last updated:** [April 13, 2022, 2:46pm UTC](https://racket.discourse.group/t/dont-export-n-th/861 "2022-04-13T14:46:27Z")
n-\>th is exported from racket/contract, and consequently by racket. However, this function is not documented, and intentionally so (racket/base.rkt at e028f252da859759100f9248230bdc4e203a6684 · racket/racket · GitHub). T… --- ## [Domain Coloring for Complex Analysis in Racket](https://racket.discourse.group/t/domain-coloring-for-complex-analysis-in-racket/877)
**Author:** [@TrueQueenBee](https://racket.discourse.group/u/TrueQueenBee)\ **Replies:** 1\ **Last updated:** [April 13, 2022, 9:45am UTC](https://racket.discourse.group/t/domain-coloring-for-complex-analysis-in-racket/877 "2022-04-13T09:45:31Z")
Hello fellow racketeers! Here is a small tool I created for drawing and analyzing complex-valued equations In the future it should be available as a package under the name domain-coloring Usage instructions and add… --- ## [Finding the type of exception](https://racket.discourse.group/t/finding-the-type-of-exception/866)
**Author:** [@robertpostill](https://racket.discourse.group/u/robertpostill)\ **Replies:** 6\ **Last updated:** [April 12, 2022, 1:12am UTC](https://racket.discourse.group/t/finding-the-type-of-exception/866 "2022-04-12T01:12:57Z")
When I'm writing around code that throws exceptions. Particularly when I'm going to wrap a side-effect in with-handlers I find myself often resorting to writing rackunit checks to find the exact type of exception being … --- ## [CLP(Rosette)-miniKanren - A miniKanren variant integrated with Rosette](https://racket.discourse.group/t/clp-rosette-minikanren-a-minikanren-variant-integrated-with-rosette/869)
**Author:** [@chansey97](https://racket.discourse.group/u/chansey97)\ **Replies:** 0\ **Last updated:** [April 9, 2022, 11:00pm UTC](https://racket.discourse.group/t/clp-rosette-minikanren-a-minikanren-variant-integrated-with-rosette/869 "2022-04-09T23:00:35Z")
Hi, I wrote a miniKanren variant integrated with Rosette. It uses Rosette (SMT) as a backend for constraints solving. Now you can use SMT assertions as constraints. It significantly improves the expressiveness of miniKa… --- ## [Finer-grained file system exceptions](https://racket.discourse.group/t/finer-grained-file-system-exceptions/870)
**Author:** [@sschwarzer](https://racket.discourse.group/u/sschwarzer)\ **Replies:** 6\ **Last updated:** [April 10, 2022, 9:29pm UTC](https://racket.discourse.group/t/finer-grained-file-system-exceptions/870 "2022-04-10T21:29:32Z")
Looking at 15.2 Filesystem , most if not all file operations, if they fail, raise exn:fail:filesystem. However, what should I do if I need more detailed information? For example, if I call rename-file-or-directory and a… --- ## [Where can I find the definition of eq? procedure](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856)
**Author:** [@otlk](https://racket.discourse.group/u/otlk)\ **Replies:** 4\ **Last updated:** [April 9, 2022, 5:04pm UTC](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856 "2022-04-09T17:04:31Z")
I am referring to the eq? procedure that is built into racket link to racket docs Things I have already tried The solution suggested here does not appear to work in my case. On right clicking eq? identifier the cont… --- ## [Help me gather keystrokes and mouse events for varied platforms](https://racket.discourse.group/t/help-me-gather-keystrokes-and-mouse-events-for-varied-platforms/307)
**Author:** [@Laurent.O](https://racket.discourse.group/u/Laurent.O)\ **Replies:** 8\ **Last updated:** [April 9, 2022, 12:45pm UTC](https://racket.discourse.group/t/help-me-gather-keystrokes-and-mouse-events-for-varied-platforms/307 "2022-04-09T12:45:01Z")
If you have a couple of minutes to spare (it shouldn't take you more than 5min in total), it would be great if you could help me gather accurate key-event% and mouse-event% for different platforms. To do so: raco pkg… --- ## [Will raco make recognize changes?](https://racket.discourse.group/t/will-raco-make-recognize-changes/864)
**Author:** [@dstorrs](https://racket.discourse.group/u/dstorrs)\ **Replies:** 1\ **Last updated:** [April 9, 2022, 1:54am UTC](https://racket.discourse.group/t/will-raco-make-recognize-changes/864 "2022-04-09T01:54:05Z")
I haven't used raco make before and I'm not sure what to expect. Does it recognize that a compiled file has changed and use the new version instead of the compiled one? If so, how? I went through the Guide and the rac… --- ## [Big-bang returns zero](https://racket.discourse.group/t/big-bang-returns-zero/862)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 1\ **Last updated:** [April 8, 2022, 4:24pm UTC](https://racket.discourse.group/t/big-bang-returns-zero/862 "2022-04-08T16:24:15Z")
I am following through the book of "Realm Of Racket" and typed in exactly as it is on the book a landing a UFO animation everything seemed to work until i put in the code for stopping the programming.Specially this part… --- ## [Question about #:grammar in defform](https://racket.discourse.group/t/question-about-grammar-in-defform/863)
**Author:** [@joskoot](https://racket.discourse.group/u/joskoot)\ **Replies:** 2\ **Last updated:** [April 8, 2022, 4:10pm UTC](https://racket.discourse.group/t/question-about-grammar-in-defform/863 "2022-04-08T16:10:53Z")
In a defform I want to produce a grammar including something like: binding = #:finish finish-id | #:finish finish-id terminator That is, clause-data consisting of more than one element. How to do that? Than… --- ## [Package Server new package workaround](https://racket.discourse.group/t/package-server-new-package-workaround/530)
**Author:** [@jbclements](https://racket.discourse.group/u/jbclements)\ **Replies:** 11\ **Last updated:** [April 8, 2022, 11:51am UTC](https://racket.discourse.group/t/package-server-new-package-workaround/530 "2022-04-08T11:51:57Z")
Preamble: with luck, this question will soon be obsolete, because someone is going to do wonderful things to the package server. Preamble 2: I know this question has been answered on the racket-users mailing list, and I… --- ## [How can i run this function/](https://racket.discourse.group/t/how-can-i-run-this-function/860)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 2\ **Last updated:** [April 8, 2022, 2:39am UTC](https://racket.discourse.group/t/how-can-i-run-this-function/860 "2022-04-08T02:39:36Z")
Hello,i have just bought this book called "realm of racket" really good book by the way ,i have learned a lot but i came across a code related to local definitions,i understand the purpose of the code and how it works bu… --- ## [Racket and DrRacket communication](https://racket.discourse.group/t/racket-and-drracket-communication/851)
**Author:** [@Junior](https://racket.discourse.group/u/Junior)\ **Replies:** 1\ **Last updated:** [April 6, 2022, 10:54pm UTC](https://racket.discourse.group/t/racket-and-drracket-communication/851 "2022-04-06T22:54:12Z")
Hello, I hope you are well ! I have a question about DrRacket and Racket. I would like to know how the two communicate. Is it in the same process or separate processes? How does it work, is it synchronous like Tree-sit… --- ## [Can't wrap my head around how to use Polymorphic functions in Typed Racket](https://racket.discourse.group/t/cant-wrap-my-head-around-how-to-use-polymorphic-functions-in-typed-racket/834)
**Author:** [@Decabytes](https://racket.discourse.group/u/Decabytes)\ **Replies:** 7\ **Last updated:** [April 4, 2022, 5:50pm UTC](https://racket.discourse.group/t/cant-wrap-my-head-around-how-to-use-polymorphic-functions-in-typed-racket/834 "2022-04-04T17:50:41Z")
I'm trying to extract the data from a xml file produced by the Tiled2D map editor. I originally had an untyped function that loaded all of this data into a Hash, but I switched to a struct because I'm not going to be ad… --- ## [Html-parsing omits end tag omission?](https://racket.discourse.group/t/html-parsing-omits-end-tag-omission/837)
**Author:** [@jjsimpso](https://racket.discourse.group/u/jjsimpso)\ **Replies:** 2\ **Last updated:** [April 4, 2022, 2:54am UTC](https://racket.discourse.group/t/html-parsing-omits-end-tag-omission/837 "2022-04-04T02:54:58Z")
The package html-parsing was recommended to me as the most accurate html parsing library in Racket. However, it doesn't appear to handle implicit end tags, which is common in a lot of html. For example, the p tags below … --- ## [Advice on implementing a contract system?](https://racket.discourse.group/t/advice-on-implementing-a-contract-system/832)
**Author:** [@LiberalArtist](https://racket.discourse.group/u/LiberalArtist)\ **Replies:** 7\ **Last updated:** [April 3, 2022, 2:07pm UTC](https://racket.discourse.group/t/advice-on-implementing-a-contract-system/832 "2022-04-03T14:07:51Z")
I'm looking for advice on beginning the implementation of a contract system (i.e. not in Racket). I've been using and contributing to Guix, an unprivileged "purely functional" package manager (and full GNU/Linux distrib… --- ## [Rackpropagator - automatic differentiation in Racket](https://racket.discourse.group/t/rackpropagator-automatic-differentiation-in-racket/844)
**Author:** [@OliverS](https://racket.discourse.group/u/OliverS)\ **Replies:** 1\ **Last updated:** [April 2, 2022, 4:44pm UTC](https://racket.discourse.group/t/rackpropagator-automatic-differentiation-in-racket/844 "2022-04-02T16:44:08Z")
I've been working on an automatic differentiation library recently and thought I'd share the current work-in-progress. I've had fun writing it and have learned a lot about the Racket macro system in the process! Rackp… --- ## [Trying to understand Racket's GUI windowing model](https://racket.discourse.group/t/trying-to-understand-rackets-gui-windowing-model/838)
**Author:** [@bmitc](https://racket.discourse.group/u/bmitc)\ **Replies:** 3\ **Last updated:** [April 2, 2022, 3:37pm UTC](https://racket.discourse.group/t/trying-to-understand-rackets-gui-windowing-model/838 "2022-04-02T15:37:17Z")
I am trying to understand Racket's GUI windowing model. I have tried reading the documentation and digging through bits of the code to understand how both windowing and event spaces are handled, but it is rather complex.… [Previous page](https://racket.discourse.group/latest.md?page=60) [Next page](https://racket.discourse.group/latest.md?page=62)