# Questions & Answers **URL:** https://racket.discourse.group/c/questions/6.md?page=1 [Latest](https://racket.discourse.group/latest.md) · [Categories](https://racket.discourse.group/categories.md) · [Tags](https://racket.discourse.group/tags.md) **Page:** 2 --- ## [Different behavior racket/base vs. racket/hash](https://racket.discourse.group/t/different-behavior-racket-base-vs-racket-hash/4198)
**Author:** [@alsch](https://racket.discourse.group/u/alsch)\ **Replies:** 6\ **Last updated:** [May 8, 2026, 3:07am UTC](https://racket.discourse.group/t/different-behavior-racket-base-vs-racket-hash/4198 "2026-05-08T03:07:12Z")
How come: #lang racket (define h (make-hash (list (list "a" 1) ) ) ) (hash-ref h "a") returns '(1) \[a list of one element\], but in Advanced Student Language: (define h (ma… --- ## [Callback from OS Thread in FFI lib](https://racket.discourse.group/t/callback-from-os-thread-in-ffi-lib/4188)
**Author:** [@hnmdijkema](https://racket.discourse.group/u/hnmdijkema)\ **Replies:** 3\ **Last updated:** [April 10, 2026, 9:53pm UTC](https://racket.discourse.group/t/callback-from-os-thread-in-ffi-lib/4188 "2026-04-10T21:53:03Z")
A question about callbacks from a C library, where the callback will be initiated from a OS thread. I'd like to initiate a callback as a kind of signal from a C library. The signal will carry one integer value. The ca… --- ## [\#lang htdp/bsl doesn't show coverage info](https://racket.discourse.group/t/lang-htdp-bsl-doesnt-show-coverage-info/4100)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 7\ **Last updated:** [April 6, 2026, 6:14pm UTC](https://racket.discourse.group/t/lang-htdp-bsl-doesnt-show-coverage-info/4100 "2026-04-06T18:14:33Z")
I've been transitioning my classes this year to use #lang htdp/bsl instead of picking a language under the menu. But I've just noticed that doing this prevents DrRacket from screaming at them about code missing coverage… --- ## [Conditional define-syntax](https://racket.discourse.group/t/conditional-define-syntax/4181)
**Author:** [@hnmdijkema](https://racket.discourse.group/u/hnmdijkema)\ **Replies:** 2\ **Last updated:** [April 5, 2026, 9:41pm UTC](https://racket.discourse.group/t/conditional-define-syntax/4181 "2026-04-05T21:41:57Z")
I'm trying to not load an FFI and define all functions when it's not available, defining the functions to be something like 'error' on call. Is it possible to do a define-syntax based on the value of a variable? e.g., s… --- ## [Images in scribbles](https://racket.discourse.group/t/images-in-scribbles/4178)
**Author:** [@hnmdijkema](https://racket.discourse.group/u/hnmdijkema)\ **Replies:** 7\ **Last updated:** [April 5, 2026, 11:51am UTC](https://racket.discourse.group/t/images-in-scribbles/4178 "2026-04-05T11:51:21Z")
I’ve got an image in a scribble, and it works in my local setup,but when I try to distributie my package, jt fails,because raco does not find it. What can I do to solve this? --- ## [Running Racket on a web server](https://racket.discourse.group/t/running-racket-on-a-web-server/3251)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 6\ **Last updated:** [April 5, 2026, 7:17am UTC](https://racket.discourse.group/t/running-racket-on-a-web-server/3251 "2026-04-05T07:17:09Z")
hello, i have this problem when trying to run a Racket application from an Apache web server. I modify a PHP application that call a command line application (could be Fortran,Python,Scheme....) the application caller … --- ## [Alias of a reader](https://racket.discourse.group/t/alias-of-a-reader/4179)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 0\ **Last updated:** [April 4, 2026, 9:23am UTC](https://racket.discourse.group/t/alias-of-a-reader/4179 "2026-04-04T09:23:38Z")
Hi, not really a question (just confirm it), i'm making an alias of a reader. i have a SRFI 105 parser which is enhanced to more than infix, also postfix and still prefix ,so instead using #lang reader SRFI-105 which i… --- ## [Linked namespaces](https://racket.discourse.group/t/linked-namespaces/4175)
**Author:** [@bdeket](https://racket.discourse.group/u/bdeket)\ **Replies:** 2\ **Last updated:** [April 3, 2026, 8:24pm UTC](https://racket.discourse.group/t/linked-namespaces/4175 "2026-04-03T20:24:06Z")
Is it possible to have linked namespaces? By which I mean that if evaluating something in namespace n1 and it is not defined in n1 it will go look for it in its parent namespace n0 (or even further if the link is longer… --- ## [Sanity check regarding #:transparent changing the value of an expression](https://racket.discourse.group/t/sanity-check-regarding-transparent-changing-the-value-of-an-expression/4172)
**Author:** [@sora22](https://racket.discourse.group/u/sora22)\ **Replies:** 5\ **Last updated:** [March 31, 2026, 9:31pm UTC](https://racket.discourse.group/t/sanity-check-regarding-transparent-changing-the-value-of-an-expression/4172 "2026-03-31T21:31:42Z")
I was recently hacking away on a function in FSM and found that adding or removing #:transparent from a struct definition caused the expression to evaluate to a different value. Without it, it goes into an infinite loop … --- ## [Racket script or executable as CGI](https://racket.discourse.group/t/racket-script-or-executable-as-cgi/4167)
**Author:** [@gritty](https://racket.discourse.group/u/gritty)\ **Replies:** 3\ **Last updated:** [March 30, 2026, 11:36pm UTC](https://racket.discourse.group/t/racket-script-or-executable-as-cgi/4167 "2026-03-30T23:36:17Z")
I am a long-time citizen of the Gemini Protocol and in that arena we use CGI and SCGI to serve dynamic content (gasp I know, but we embrace it - check the link). I created a SCGI server in Racket to serve a basic client… --- ## [RSound and libportaudio-2.dll](https://racket.discourse.group/t/rsound-and-libportaudio-2-dll/2678)
**Author:** [@matteo-daddio](https://racket.discourse.group/u/matteo-daddio)\ **Replies:** 17\ **Last updated:** [March 30, 2026, 3:45am UTC](https://racket.discourse.group/t/rsound-and-libportaudio-2-dll/2678 "2026-03-30T03:45:04Z")
Hello, I'm trying to work with sounds and I installed the RSound package. When I try to run: (require rsound) (play ding) the result is an error: I found the libportaudio-2.dll on dll-files.com. I tried to copy i… --- ## [How hard would it be to get signatures for 2htdp/image?](https://racket.discourse.group/t/how-hard-would-it-be-to-get-signatures-for-2htdp-image/3309)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 11\ **Last updated:** [March 29, 2026, 10:28am UTC](https://racket.discourse.group/t/how-hard-would-it-be-to-get-signatures-for-2htdp-image/3309 "2026-03-29T10:28:54Z")
Given that Beginning Student has support for signatures, how hard would it be to allow Image, Color, etc as types so that signatures could be used with image functions? --- ## [Why does the stacktrace stops short of the error?](https://racket.discourse.group/t/why-does-the-stacktrace-stops-short-of-the-error/4169)
**Author:** [@MickeyKnox](https://racket.discourse.group/u/MickeyKnox)\ **Replies:** 1\ **Last updated:** [March 27, 2026, 11:56pm UTC](https://racket.discourse.group/t/why-does-the-stacktrace-stops-short-of-the-error/4169 "2026-03-27T23:56:42Z")
I've created a minimal example for a nasty error I had: #lang racket (require "foo.rkt") (module+ main (run)) (define (run) (error-fun 7)) and foo.rkt: #lang racket (provide error-fun) (struct foo (num)) (de… --- ## [Signatures in student languages](https://racket.discourse.group/t/signatures-in-student-languages/4166)
**Author:** [@bugcounting](https://racket.discourse.group/u/bugcounting)\ **Replies:** 6\ **Last updated:** [March 26, 2026, 5:33pm UTC](https://racket.discourse.group/t/signatures-in-student-languages/4166 "2026-03-26T17:33:08Z")
Hi all, I've been following HtDP to teach introductory programming at USI Lugano for several years now, and I really like the approach. The one thing that I have been missing from the student languages is some kind of s… --- ## [Improving DrRacket ergonomics](https://racket.discourse.group/t/improving-drracket-ergonomics/4163)
**Author:** [@xerz](https://racket.discourse.group/u/xerz)\ **Replies:** 3\ **Last updated:** [March 24, 2026, 8:34pm UTC](https://racket.discourse.group/t/improving-drracket-ergonomics/4163 "2026-03-24T20:34:06Z")
Heya there! So I've been casually looking at the Racket ecosystem for a year or so, and due to recent circumstances I'm now planning to do HtDP, just so I can tick it off from my todo list and see if there's something I … --- ## [Any way to set preferences programmatically?](https://racket.discourse.group/t/any-way-to-set-preferences-programmatically/4165)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 4\ **Last updated:** [March 24, 2026, 2:58pm UTC](https://racket.discourse.group/t/any-way-to-set-preferences-programmatically/4165 "2026-03-24T14:58:24Z")
I had an epiphany recently. There are things I want students to have set up whenever they're working on my assignments. I love using signatures, but need to include the Image signature and related if I want to do image… --- ## [Unloading a C library / reinitializing (FFI)](https://racket.discourse.group/t/unloading-a-c-library-reinitializing-ffi/4147)
**Author:** [@hnmdijkema](https://racket.discourse.group/u/hnmdijkema)\ **Replies:** 12\ **Last updated:** [March 23, 2026, 12:38pm UTC](https://racket.discourse.group/t/unloading-a-c-library-reinitializing-ffi/4147 "2026-03-23T12:38:53Z")
Suppose I would like to unload a library (QtWebEngine) as to re-initialize the complete structure as if loaded for the first time. Would that be possible with racket? Otherwise are there handlers to make it possible to … --- ## [Send to REPL and multi-module projects](https://racket.discourse.group/t/send-to-repl-and-multi-module-projects/4146)
**Author:** [@alexsh](https://racket.discourse.group/u/alexsh)\ **Replies:** 31\ **Last updated:** [March 20, 2026, 2:22am UTC](https://racket.discourse.group/t/send-to-repl-and-multi-module-projects/4146 "2026-03-20T02:22:01Z")
Originally asked here: Send to REPL and multi-module projects · Issue #766 · greghendershott/racket-mode · GitHub Hi! I am starting a project where I will have many module files, but it seems that "send to REPL" functi… --- ## [Equal?/recur examples](https://racket.discourse.group/t/equal-recur-examples/4143)
**Author:** [@matteo-daddio](https://racket.discourse.group/u/matteo-daddio)\ **Replies:** 3\ **Last updated:** [March 14, 2026, 9:50am UTC](https://racket.discourse.group/t/equal-recur-examples/4143 "2026-03-14T09:50:14Z")
Hello, reading the racket guide I found the equal?/recur function. I find difficult to understand how it works. Does somebody have some interesting examples? Thank you Matteo --- ## [Way to use \`empty\` instead of \`'()\`, at least until I introduce \`(quote ...)\` and \`'(...)\`?](https://racket.discourse.group/t/way-to-use-empty-instead-of-at-least-until-i-introduce-quote-and/4133)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 14\ **Last updated:** [March 11, 2026, 2:44am UTC](https://racket.discourse.group/t/way-to-use-empty-instead-of-at-least-until-i-introduce-quote-and/4133 "2026-03-11T02:44:34Z")
Is there a parameter or anything I can use to have '() print as empty, as it used to, in the latest versions of DrRacket. I've searched around, but couldn't find anything. I'd just like to hold off on '() until I've tau… --- ## [Why does this continuation return twice?](https://racket.discourse.group/t/why-does-this-continuation-return-twice/4138)
**Author:** [@nealburns5](https://racket.discourse.group/u/nealburns5)\ **Replies:** 4\ **Last updated:** [March 10, 2026, 1:54pm UTC](https://racket.discourse.group/t/why-does-this-continuation-return-twice/4138 "2026-03-10T13:54:49Z")
Why do I get 2 return values when I run this from the repl? #lang racket (require db racket/pretty racket/control) (define (make-query-func db-path) (define conn (sqlite3-connect #:database db-path … --- ## [Install docs for a user-scope package that creates collections under an installation-scope package](https://racket.discourse.group/t/install-docs-for-a-user-scope-package-that-creates-collections-under-an-installation-scope-package/4137)
**Author:** [@benknoble](https://racket.discourse.group/u/benknoble)\ **Replies:** 2\ **Last updated:** [March 8, 2026, 3:09pm UTC](https://racket.discourse.group/t/install-docs-for-a-user-scope-package-that-creates-collections-under-an-installation-scope-package/4137 "2026-03-08T15:09:24Z")
Concretely, gui-easy has collections racket/gui/easy, so: # raco setup --pkgs gui-easy raco setup: version: 8.17 raco setup: platform: x86\_64-linux \[cs\] raco setup: target machine: ta6le raco setup: installation name: 8… --- ## [Getting the port number of serve/servlet when running on an ephemeral port](https://racket.discourse.group/t/getting-the-port-number-of-serve-servlet-when-running-on-an-ephemeral-port/4130)
**Author:** [@hnmdijkema](https://racket.discourse.group/u/hnmdijkema)\ **Replies:** 4\ **Last updated:** [March 8, 2026, 2:52pm UTC](https://racket.discourse.group/t/getting-the-port-number-of-serve-servlet-when-running-on-an-ephemeral-port/4130 "2026-03-08T14:52:49Z")
Dear all, I've trouble finding this in the documentation. Suppose I start the racket web framework as follows: (serve/servlet (λ (req) (web-serve h req)) #:listen-ip "127.0.0.1" … --- ## [Emulating Python's zip function with variadic input](https://racket.discourse.group/t/emulating-pythons-zip-function-with-variadic-input/4135)
**Author:** [@gritty](https://racket.discourse.group/u/gritty)\ **Replies:** 4\ **Last updated:** [March 7, 2026, 11:33pm UTC](https://racket.discourse.group/t/emulating-pythons-zip-function-with-variadic-input/4135 "2026-03-07T23:33:38Z")
Hello, first post here, and I'm quite new to Racket. I searched the above question in previous answers but didn't find anything. What I'm trying to achieve: basically a for/list with a variadic input. Example: (defin… --- ## [Loop of restore previous files craziness](https://racket.discourse.group/t/loop-of-restore-previous-files-craziness/4116)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 15\ **Last updated:** [March 6, 2026, 6:37pm UTC](https://racket.discourse.group/t/loop-of-restore-previous-files-craziness/4116 "2026-03-06T18:37:06Z")
This happened in class today. I created a small file that exports some stuff and renames signatures from deinprogramm/sdp/image.rkt to match the upper-case style that BSL uses. Things seemed to be working okay (except … --- ## [You can't use local in BSL. :-(](https://racket.discourse.group/t/you-cant-use-local-in-bsl/4127)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 5\ **Last updated:** [March 3, 2026, 1:32pm UTC](https://racket.discourse.group/t/you-cant-use-local-in-bsl/4127 "2026-03-03T13:32:50Z")
I don't know if this is a feature request or just a whine, but I would love to be able to introduce local before list abbreviations. Unfortunately, you can't use local in BSL, because the macro raises an error if you ha… --- ## [Scribble-math package installation error](https://racket.discourse.group/t/scribble-math-package-installation-error/3749)
**Author:** [@encomer](https://racket.discourse.group/u/encomer)\ **Replies:** 17\ **Last updated:** [February 24, 2026, 8:11am UTC](https://racket.discourse.group/t/scribble-math-package-installation-error/3749 "2026-02-24T08:11:55Z")
While trying to (re)install the scribble-math package (using the Package Manager, under DrRacket), currently I get the following error: Downloading repository https://gitea.suzanne.soy/suzanne.soy/scribble-math.git#main… --- ## [Coverage weirdness in \`define-struct\`](https://racket.discourse.group/t/coverage-weirdness-in-define-struct/4117)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 3\ **Last updated:** [February 21, 2026, 1:35am UTC](https://racket.discourse.group/t/coverage-weirdness-in-define-struct/4117 "2026-02-21T01:35:07Z")
So the fields in structs are marked as uncovered, even if you use selectors to access them. After running the definitions, name and grade are marked as uncovered. I'm pretty sure this is a regression of some sort. --- ## [Can't get .rkt file to publish with Pollen?](https://racket.discourse.group/t/cant-get-rkt-file-to-publish-with-pollen/4101)
**Author:** [@ToddOBryan](https://racket.discourse.group/u/ToddOBryan)\ **Replies:** 2\ **Last updated:** [February 20, 2026, 12:23am UTC](https://racket.discourse.group/t/cant-get-rkt-file-to-publish-with-pollen/4101 "2026-02-20T00:23:09Z")
I'm doing my class website with Pollen, but I ran into a weird issue today. I needed to include a .rkt file for students to download, but couldn't get Pollen to include it with the raco pollen publish command. I suspect … --- ## [Bug in package building and web site](https://racket.discourse.group/t/bug-in-package-building-and-web-site/4090)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 7\ **Last updated:** [February 16, 2026, 6:59am UTC](https://racket.discourse.group/t/bug-in-package-building-and-web-site/4090 "2026-02-16T06:59:24Z")
Hi, when updating Scheme+ the package system initially failed to build the package because doc had an error: if i insert an image in the doc, which is rarely done but feature exists, then if i put the image in the scri… [Previous page](https://racket.discourse.group/c/questions/6.md) [Next page](https://racket.discourse.group/c/questions/6.md?page=2)