# Questions & Answers **URL:** https://racket.discourse.group/c/questions/6.md?page=6 [Latest](https://racket.discourse.group/latest.md) · [Categories](https://racket.discourse.group/categories.md) · [Tags](https://racket.discourse.group/tags.md) **Page:** 7 --- ## [DrRacket setup for learning The Little Schemer](https://racket.discourse.group/t/drracket-setup-for-learning-the-little-schemer/3705)
**Author:** [@code2018](https://racket.discourse.group/u/code2018)\ **Replies:** 3\ **Last updated:** [April 28, 2025, 5:06pm UTC](https://racket.discourse.group/t/drracket-setup-for-learning-the-little-schemer/3705 "2025-04-28T17:06:48Z")
As the title says - are there links/docs to the basic setup as I would like to get started on the book (which I have been planning for a while) --- ## [Question about syntax](https://racket.discourse.group/t/question-about-syntax/3697)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 4\ **Last updated:** [April 21, 2025, 8:07pm UTC](https://racket.discourse.group/t/question-about-syntax/3697 "2025-04-21T20:07:50Z")
Hi, i have this code : ;; operators (cond ((char=? c #\\+) (define n (string-\>number p-tok)) ; partial token is completed (if n (return (cons n (cons #'+ (parse-superscript-tok… --- ## [Can Typed Racket Treat Types as Runtime Values?](https://racket.discourse.group/t/can-typed-racket-treat-types-as-runtime-values/3696)
**Author:** [@NoahStoryM](https://racket.discourse.group/u/NoahStoryM)\ **Replies:** 0\ **Last updated:** [April 20, 2025, 4:34am UTC](https://racket.discourse.group/t/can-typed-racket-treat-types-as-runtime-values/3696 "2025-04-20T04:34:05Z")
I want to refine types without relying on predicates, so I attempted to implement ⊔, ann\* and type-case. Here are usage examples of these operators: (: flexible-length (→ (⊔ String (Listof Any)) Index)) (define (flexibl… --- ## [Exporting a struct invariant contract](https://racket.discourse.group/t/exporting-a-struct-invariant-contract/3694)
**Author:** [@KevinW](https://racket.discourse.group/u/KevinW)\ **Replies:** 2\ **Last updated:** [April 18, 2025, 10:23pm UTC](https://racket.discourse.group/t/exporting-a-struct-invariant-contract/3694 "2025-04-18T22:23:45Z")
Hi, I'm trying to create a struct with a contract that involves a relationship between two fields. The struct needs to be exported. It seems like what I need is an "invariant contract" as in struct/dc: 8.1 Data-structur… --- ## [How to Design Worlds](https://racket.discourse.group/t/how-to-design-worlds/3693)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 1\ **Last updated:** [April 17, 2025, 12:41pm UTC](https://racket.discourse.group/t/how-to-design-worlds/3693 "2025-04-17T12:41:45Z")
Is the source for How to Design Worlds available anywhere? I think it's somewhat out of date, but I'd like to update it and make it available to my students. --- ## [Macro based contracts](https://racket.discourse.group/t/macro-based-contracts/3691)
**Author:** [@sora22](https://racket.discourse.group/u/sora22)\ **Replies:** 0\ **Last updated:** [April 15, 2025, 9:47pm UTC](https://racket.discourse.group/t/macro-based-contracts/3691 "2025-04-15T21:47:28Z")
A few years ago Robby mentioned that if he could get to redo racket contracts that he'd use macros instead here Are any of you aware if there has been any work done towards this idea? --- ## [Cannot enter https://racket-lang.org/](https://racket.discourse.group/t/cannot-enter-https-racket-lang-org/3690)
**Author:** [@joskoot](https://racket.discourse.group/u/joskoot)\ **Replies:** 3\ **Last updated:** [April 13, 2025, 10:13pm UTC](https://racket.discourse.group/t/cannot-enter-https-racket-lang-org/3690 "2025-04-13T22:13:11Z")
Is there a problem? I have no problems with other web pages. Thanks, Jos --- ## [Single Percision Float on Chez-Scheme impl](https://racket.discourse.group/t/single-percision-float-on-chez-scheme-impl/3687)
**Author:** [@xiaoyu2006](https://racket.discourse.group/u/xiaoyu2006)\ **Replies:** 1\ **Last updated:** [April 13, 2025, 9:58am UTC](https://racket.discourse.group/t/single-percision-float-on-chez-scheme-impl/3687 "2025-04-13T09:58:14Z")
A part of my Racket program requires calculating single-precision float number that follows IEEE 754. However my Racket tells me (single-flonum-available?) ; =\> #f. How can I bypass this? I imagine I can have such api (… --- ## [Extending the reader to support Kawa-like treatment of colons](https://racket.discourse.group/t/extending-the-reader-to-support-kawa-like-treatment-of-colons/3676)
**Author:** [@panicz](https://racket.discourse.group/u/panicz)\ **Replies:** 5\ **Last updated:** [April 5, 2025, 3:02pm UTC](https://racket.discourse.group/t/extending-the-reader-to-support-kawa-like-treatment-of-colons/3676 "2025-04-05T15:02:45Z")
I posted this message on google groups before learning that it's (likely) no longer used, so I'm cross-posting it here: I've had an idea to implement a #lang that would provide some syntactic extensions akin to those pr… --- ## [MariaDB/MySQL database connexion error](https://racket.discourse.group/t/mariadb-mysql-database-connexion-error/3674)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 6\ **Last updated:** [April 4, 2025, 1:23pm UTC](https://racket.discourse.group/t/mariadb-mysql-database-connexion-error/3674 "2025-04-04T13:23:13Z")
Hi, i'm sticked on this database connexion error when i do: (require db) ; for database connectivity (mysql-connect #:user "mattei") . . ../../../../Applications/Racket v8.14/collects/racket/private/kw.rkt:1313:23: mys… --- ## [Could you Provide your Opinions about the Racket Language ..Both good and bad](https://racket.discourse.group/t/could-you-provide-your-opinions-about-the-racket-language-both-good-and-bad/3653)
**Author:** [@Chocolate-ux](https://racket.discourse.group/u/Chocolate-ux)\ **Replies:** 7\ **Last updated:** [April 3, 2025, 12:57pm UTC](https://racket.discourse.group/t/could-you-provide-your-opinions-about-the-racket-language-both-good-and-bad/3653 "2025-04-03T12:57:01Z")
Could u provide your opinions on the racket language Strengths 1.Educational Value 2.Simple and consistent syntax 3.Promotes Language-Oriented Programming 4.Robust Standard Library 5.Strong Support for Functional P… --- ## [How do I install a local version of scribble, without cloning?](https://racket.discourse.group/t/how-do-i-install-a-local-version-of-scribble-without-cloning/3640)
**Author:** [@stevebyan](https://racket.discourse.group/u/stevebyan)\ **Replies:** 14\ **Last updated:** [March 31, 2025, 4:47pm UTC](https://racket.discourse.group/t/how-do-i-install-a-local-version-of-scribble-without-cloning/3640 "2025-03-31T16:47:18Z")
I'm using Racket v8.16 on macOS Sequoia. I'm getting back to hacking scribble after 9 months. I had installed a local git clone of scribble in v8.14. I updated to v8.16 by simply installing the distribution. Of course th… --- ## [Reference on "A language to create documents"](https://racket.discourse.group/t/reference-on-a-language-to-create-documents/3661)
**Author:** [@aanastasiou](https://racket.discourse.group/u/aanastasiou)\ **Replies:** 2\ **Last updated:** [March 27, 2025, 5:37pm UTC](https://racket.discourse.group/t/reference-on-a-language-to-create-documents/3661 "2025-03-27T17:37:44Z")
Hello A few months ago there was a post about a new language that was used to create documents and that language was based on Racket. The linked post was going on about the need to create a language to handle this task… --- ## [How to set up definitions (as in LaTeX) in scribble?](https://racket.discourse.group/t/how-to-set-up-definitions-as-in-latex-in-scribble/3654)
**Author:** [@danielittlewood](https://racket.discourse.group/u/danielittlewood)\ **Replies:** 6\ **Last updated:** [March 27, 2025, 4:36pm UTC](https://racket.discourse.group/t/how-to-set-up-definitions-as-in-latex-in-scribble/3654 "2025-03-27T16:36:58Z")
I am trying to use scribble to write a technical document, with "defined terms". I would like in one place to be able to make a definition and give it a tag, and then refer to that tag elsewhere (perhaps in the same doc,… --- ## [DrRacket and Scribble datums](https://racket.discourse.group/t/drracket-and-scribble-datums/3659)
**Author:** [@stevebyan](https://racket.discourse.group/u/stevebyan)\ **Replies:** 5\ **Last updated:** [March 27, 2025, 1:03am UTC](https://racket.discourse.group/t/drracket-and-scribble-datums/3659 "2025-03-27T01:03:07Z")
How do I persuade DrRacket to let me type an opening square bracket to introduce a datum after the command, as in this example from the Scribble docs: @foo\[#:width 2\]{blah blah} It insists on inserting an open parenthes… --- ## [Mocking system effectively](https://racket.discourse.group/t/mocking-system-effectively/3643)
**Author:** [@robertpostill](https://racket.discourse.group/u/robertpostill)\ **Replies:** 7\ **Last updated:** [March 26, 2025, 9:47am UTC](https://racket.discourse.group/t/mocking-system-effectively/3643 "2025-03-26T09:47:07Z")
I'm trying to mock a side-effect-riddled process. Part of this is to wrap a call to ifconfig. The code I'm wrapping looks like this: (define (get-mac-address #:ifconfig-invoker \[system system\]) (define mac-address-r… --- ## [How can I access the author and date in \`html-render:render-one-part\`?](https://racket.discourse.group/t/how-can-i-access-the-author-and-date-in-html-render-render-one-part/3650)
**Author:** [@stevebyan](https://racket.discourse.group/u/stevebyan)\ **Replies:** 1\ **Last updated:** [March 25, 2025, 5:54pm UTC](https://racket.discourse.group/t/how-can-i-access-the-author-and-date-in-html-render-render-one-part/3650 "2025-03-25T17:54:20Z")
I'm trying to access the author(s) and date in the render-one-part method in html-render.rkt. I've added extract-date to the list of methods inherited from the render-mixin. extract-authors is already there. However, ca… --- ## [Some small improvements to signatures](https://racket.discourse.group/t/some-small-improvements-to-signatures/3619)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 7\ **Last updated:** [March 23, 2025, 12:09am UTC](https://racket.discourse.group/t/some-small-improvements-to-signatures/3619 "2025-03-23T00:09:49Z")
I noticed that in the latest version of the docs for BSL, signatures get a mention. Thank you! There are a couple of small pain points before I can use them, however. Could we provide a link to the list of Signatures… --- ## [How to test scribble?](https://racket.discourse.group/t/how-to-test-scribble/3642)
**Author:** [@stevebyan](https://racket.discourse.group/u/stevebyan)\ **Replies:** 0\ **Last updated:** [March 22, 2025, 2:47pm UTC](https://racket.discourse.group/t/how-to-test-scribble/3642 "2025-03-22T14:47:29Z")
Are there additional tests for scribble beyond raco test -c scribble? --- ## [Best way to integrate "schemesh" written in Chez Scheme, into Racket ecosystem?](https://racket.discourse.group/t/best-way-to-integrate-schemesh-written-in-chez-scheme-into-racket-ecosystem/3629)
**Author:** [@Cosmos721](https://racket.discourse.group/u/Cosmos721)\ **Replies:** 8\ **Last updated:** [March 22, 2025, 8:43am UTC](https://racket.discourse.group/t/best-way-to-integrate-schemesh-written-in-chez-scheme-into-racket-ecosystem/3629 "2025-03-22T08:43:55Z")
I would like to extend my program schemesh, currently written in Chez Scheme, and integrate it within Racket ecosystem. A little background to explain the question: schemesh is a Unix shell scriptable in Chez Scheme. … --- ## [How to get a list of query parameters of request using web-server/http/request-structs](https://racket.discourse.group/t/how-to-get-a-list-of-query-parameters-of-request-using-web-server-http-request-structs/3627)
**Author:** [@rvdalen](https://racket.discourse.group/u/rvdalen)\ **Replies:** 9\ **Last updated:** [March 16, 2025, 9:06pm UTC](https://racket.discourse.group/t/how-to-get-a-list-of-query-parameters-of-request-using-web-server-http-request-structs/3627 "2025-03-16T21:06:28Z")
I am trying to get my head around writing simple web applications in Racket. How do I get a list of query parameters sent as part of the request from the request struct, assuming the servlet below: (define (first-page … --- ## [How to attach an exception to a syntactic location?](https://racket.discourse.group/t/how-to-attach-an-exception-to-a-syntactic-location/3631)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 0\ **Last updated:** [March 16, 2025, 4:50pm UTC](https://racket.discourse.group/t/how-to-attach-an-exception-to-a-syntactic-location/3631 "2025-03-16T16:50:35Z")
Following along with Beautiful Racket, I'm trying to implement the AP Computer Science Principles pseudo-code that is used on the exam. So far, so good. Except that I'd like to have errors attach to the locations in t… --- ## [Are signatures supported in non-teaching languages?](https://racket.discourse.group/t/are-signatures-supported-in-non-teaching-languages/3623)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 2\ **Last updated:** [March 14, 2025, 1:00pm UTC](https://racket.discourse.group/t/are-signatures-supported-in-non-teaching-languages/3623 "2025-03-14T13:00:48Z")
I wanted to create a files students could require and thought I'd include signatures in case some precocious students look at the file. Is there support for (: name (input -\> output)) in some module I can require? Usin… --- ## [Can Racket send simulated keystrokes to the OS?](https://racket.discourse.group/t/can-racket-send-simulated-keystrokes-to-the-os/490)
**Author:** [@joeld](https://racket.discourse.group/u/joeld)\ **Replies:** 5\ **Last updated:** [March 12, 2025, 9:15am UTC](https://racket.discourse.group/t/can-racket-send-simulated-keystrokes-to-the-os/490 "2025-03-12T09:15:46Z")
Is it possible for a Racket program to send keystrokes to the current app in a desktop environment? Wondering if I can substitute a Racket program/DSL for for Autohotkey, which is atrocious. --- ## [Partially override gen:custom-write for the display case only](https://racket.discourse.group/t/partially-override-gen-custom-write-for-the-display-case-only/3616)
**Author:** [@rvdalen](https://racket.discourse.group/u/rvdalen)\ **Replies:** 2\ **Last updated:** [March 11, 2025, 4:32am UTC](https://racket.discourse.group/t/partially-override-gen-custom-write-for-the-display-case-only/3616 "2025-03-11T04:32:59Z")
I am trying to customize the printing of a struct for the display case to something that displays more user-friendly but I am not sure how to express: "do the default action for print and write cases". Here is the code … --- ## [Allocating a pointer to an array of C structs using C FFI](https://racket.discourse.group/t/allocating-a-pointer-to-an-array-of-c-structs-using-c-ffi/3615)
**Author:** [@jjsimpso](https://racket.discourse.group/u/jjsimpso)\ **Replies:** 0\ **Last updated:** [March 10, 2025, 3:09pm UTC](https://racket.discourse.group/t/allocating-a-pointer-to-an-array-of-c-structs-using-c-ffi/3615 "2025-03-10T15:09:12Z")
I'd like suggestions for improving the following function: (define-cstruct \_Slice (\[start \_intptr\] \[end \_intptr\] \[stride \_intptr\])) ;; provide the number of dimensions and a list of triples(start end stride) ;;… --- ## [Continuation with multiple values](https://racket.discourse.group/t/continuation-with-multiple-values/3614)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 2\ **Last updated:** [March 10, 2025, 5:41am UTC](https://racket.discourse.group/t/continuation-with-multiple-values/3614 "2025-03-10T05:41:46Z")
Hello, just an (expert) question , is there a way in call/cc to return multiple values? i mean something like this but working: \> (call/cc (lambda (ct) (ct (values 1 2)))) . . result arity mismatch; expected number o… --- ## [Broken record-update behaviour in SRFI-57](https://racket.discourse.group/t/broken-record-update-behaviour-in-srfi-57/3613)
**Author:** [@dguthrie](https://racket.discourse.group/u/dguthrie)\ **Replies:** 0\ **Last updated:** [March 9, 2025, 12:09pm UTC](https://racket.discourse.group/t/broken-record-update-behaviour-in-srfi-57/3613 "2025-03-09T12:09:03Z")
I'm trying to use SRFI 57 (the extended record types). According to the documentation, SRFI 57 is supported and indeed it appears to be built in to Racket. This is with #lang racket and (require srfi/57) as preamble. SR… --- ## [How to create a minimal racket?](https://racket.discourse.group/t/how-to-create-a-minimal-racket/3603)
**Author:** [@YongaTechnic](https://racket.discourse.group/u/YongaTechnic)\ **Replies:** 1\ **Last updated:** [March 4, 2025, 2:47pm UTC](https://racket.discourse.group/t/how-to-create-a-minimal-racket/3603 "2025-03-04T14:47:34Z")
I want to create a stripped down version of racket, which only includes the module system macro system and the contracts? Is there such a version of it? Or is there a way to make such a release? If someone can also ans… --- ## [Trouble keeping types constrained in typed racket](https://racket.discourse.group/t/trouble-keeping-types-constrained-in-typed-racket/3598)
**Author:** [@sora22](https://racket.discourse.group/u/sora22)\ **Replies:** 6\ **Last updated:** [March 4, 2025, 1:23am UTC](https://racket.discourse.group/t/trouble-keeping-types-constrained-in-typed-racket/3598 "2025-03-04T01:23:21Z")
I'm currently working with context free grammars at the moment, and have a need to find membership within grammars in chomsky normal form as efficiently as possible. I know typed racket could possibly provide some optimi… [Previous page](https://racket.discourse.group/c/questions/6.md?page=5) [Next page](https://racket.discourse.group/c/questions/6.md?page=7)