# Questions & Answers **URL:** https://racket.discourse.group/c/questions/6.md?page=24 [Latest](https://racket.discourse.group/latest.md) · [Categories](https://racket.discourse.group/categories.md) · [Tags](https://racket.discourse.group/tags.md) **Page:** 25 --- ## [Racket package online seems not to rebuild my package](https://racket.discourse.group/t/racket-package-online-seems-not-to-rebuild-my-package/1500)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 6\ **Last updated:** [November 19, 2022, 3:03am UTC](https://racket.discourse.group/t/racket-package-online-seems-not-to-rebuild-my-package/1500 "2022-11-19T03:03:34Z")
hello, my last rebuil is 2 days ago, one was sheduled this morning (european time) but no news? is it normal? best regards, damien --- ## [Adding a new \`raco\` command - path configuration](https://racket.discourse.group/t/adding-a-new-raco-command-path-configuration/1488)
**Author:** [@soegaard](https://racket.discourse.group/u/soegaard)\ **Replies:** 2\ **Last updated:** [November 17, 2022, 9:22pm UTC](https://racket.discourse.group/t/adding-a-new-raco-command-path-configuration/1488 "2022-11-17T21:22:55Z")
Hi All, In an attempt to make the Racket package pyffi easier to configure, I added a raco command, so users can write raco pyffi configure to start a configuration tool. Now, I have tested this on my own machine and … --- ## [I need help with this exercise in DrRacket](https://racket.discourse.group/t/i-need-help-with-this-exercise-in-drracket/1494)
**Author:** [@CelsoBorges360](https://racket.discourse.group/u/CelsoBorges360)\ **Replies:** 2\ **Last updated:** [November 17, 2022, 9:02pm UTC](https://racket.discourse.group/t/i-need-help-with-this-exercise-in-drracket/1494 "2022-11-17T21:02:31Z")
Hello, I'm trying to solve this exercise but I can't Consider the recurrence relation: Write a tail recursive function that calculate the nth term of the sequence, with the starting initials: 𝑎0 = 𝑎1 = 1 for examp… --- ## [Can someone help me with this exercise in DrRacket?](https://racket.discourse.group/t/can-someone-help-me-with-this-exercise-in-drracket/1495)
**Author:** [@JohanVenegas](https://racket.discourse.group/u/JohanVenegas)\ **Replies:** 2\ **Last updated:** [November 17, 2022, 9:01pm UTC](https://racket.discourse.group/t/can-someone-help-me-with-this-exercise-in-drracket/1495 "2022-11-17T21:01:30Z")
--- ## [Questions on quoting](https://racket.discourse.group/t/questions-on-quoting/1472)
**Author:** [@sschwarzer](https://racket.discourse.group/u/sschwarzer)\ **Replies:** 14\ **Last updated:** [November 17, 2022, 6:25am UTC](https://racket.discourse.group/t/questions-on-quoting/1472 "2022-11-17T06:25:22Z")
Disclaimer: The following questions are not relevant for any code I'm working on, but I'm curious about any answers, since I'm still wondering about these questions despite telling me repeatedly they're not important. … --- ## [Mutable hash sets in typed Racket](https://racket.discourse.group/t/mutable-hash-sets-in-typed-racket/1452)
**Author:** [@hendrikboom3](https://racket.discourse.group/u/hendrikboom3)\ **Replies:** 0\ **Last updated:** [November 11, 2022, 3:22pm UTC](https://racket.discourse.group/t/mutable-hash-sets-in-typed-racket/1452 "2022-11-11T15:22:55Z")
Mutable sets seem to be in Racket. However, in typed Racket, the Setof type constructor's description explicitly rejects mutable sets. And the regular Racket operation mutable-seteq seems to be unavailable. Is this tr… --- ## [Metapict questions on filling polygons from points](https://racket.discourse.group/t/metapict-questions-on-filling-polygons-from-points/1449)
**Author:** [@pmatos](https://racket.discourse.group/u/pmatos)\ **Replies:** 4\ **Last updated:** [November 10, 2022, 10:34am UTC](https://racket.discourse.group/t/metapict-questions-on-filling-polygons-from-points/1449 "2022-11-10T10:34:45Z")
I am trying to draw something in metapict and I am having trouble simplifying code. Lets say I have 2 rectangles side by side, roughly: A B C x------------x------------x | | … --- ## [What section of the docs would you like more examples for?](https://racket.discourse.group/t/what-section-of-the-docs-would-you-like-more-examples-for/1427)
**Author:** [@dstorrs](https://racket.discourse.group/u/dstorrs)\ **Replies:** 7\ **Last updated:** [November 2, 2022, 9:02pm UTC](https://racket.discourse.group/t/what-section-of-the-docs-would-you-like-more-examples-for/1427 "2022-11-02T21:02:17Z")
I'm volunteering to add examples and expanded text to the Racket documentation. What would be some high-value areas to do that in? Are there particular segments of the docs that you've found hard to understand? Let me… --- ## [Wrap a macro injecting bindings in another macro](https://racket.discourse.group/t/wrap-a-macro-injecting-bindings-in-another-macro/1406)
**Author:** [@scolobb](https://racket.discourse.group/u/scolobb)\ **Replies:** 4\ **Last updated:** [November 2, 2022, 5:49pm UTC](https://racket.discourse.group/t/wrap-a-macro-injecting-bindings-in-another-macro/1406 "2022-11-02T17:49:03Z")
Hi, I have in my toolbox the macro auto-hash-ref/:, defined here. Essentially, the idea is to automatically search for a variable value in a hash table. For example: (define ht (hash 'a 1 'b 2)) (auto-hash-ref/: ht (… --- ## [How to turn a list into a hash table?](https://racket.discourse.group/t/how-to-turn-a-list-into-a-hash-table/1429)
**Author:** [@greg](https://racket.discourse.group/u/greg)\ **Replies:** 2\ **Last updated:** [October 31, 2022, 11:27pm UTC](https://racket.discourse.group/t/how-to-turn-a-list-into-a-hash-table/1429 "2022-10-31T23:27:55Z")
hi guys! i recently started learning racket and still wrestle with some basic constructs. how can i write something like this: (list-to-hashtable (list (λ (list-item) (create-hashtable-key-from-list-item list-item)))) … --- ## [FFI wrapper for a callback with variable number of arguments](https://racket.discourse.group/t/ffi-wrapper-for-a-callback-with-variable-number-of-arguments/1416)
**Author:** [@wluker](https://racket.discourse.group/u/wluker)\ **Replies:** 2\ **Last updated:** [October 31, 2022, 2:11pm UTC](https://racket.discourse.group/t/ffi-wrapper-for-a-callback-with-variable-number-of-arguments/1416 "2022-10-31T14:11:08Z")
In the GEOS C library a variadic printf like function is required as a callback for error reporting and I am unsure how to wrap that with racket's FFI. There is a racket ffi example of how to wrap printf where the types… --- ## [Always on top, racket/gui frame](https://racket.discourse.group/t/always-on-top-racket-gui-frame/1423)
**Author:** [@tehkonst](https://racket.discourse.group/u/tehkonst)\ **Replies:** 2\ **Last updated:** [October 31, 2022, 12:30am UTC](https://racket.discourse.group/t/always-on-top-racket-gui-frame/1423 "2022-10-31T00:30:37Z")
How can I make the frame window from racket/gui to be "pinned" always on top? --- ## [Preserving original numerator/denominator](https://racket.discourse.group/t/preserving-original-numerator-denominator/1414)
**Author:** [@joeld](https://racket.discourse.group/u/joeld)\ **Replies:** 1\ **Last updated:** [October 26, 2022, 1:57pm UTC](https://racket.discourse.group/t/preserving-original-numerator-denominator/1414 "2022-10-26T13:57:33Z")
Idle question: is there a way to preserve the original numerator and denominator of an exact integer when entered as a ratio? For example, 4/12 evaluates to 1/3 and (numerator 4/12) returns 1, but is it possible to get 4 … --- ## [Structs and Keywords](https://racket.discourse.group/t/structs-and-keywords/1399)
**Author:** [@denis](https://racket.discourse.group/u/denis)\ **Replies:** 10\ **Last updated:** [October 26, 2022, 12:51pm UTC](https://racket.discourse.group/t/structs-and-keywords/1399 "2022-10-26T12:51:38Z")
Coming back to learning Racket after a bit of a pause---I've just realized that Racket does not seem to have native support for keyword assignment in structs. Is that still the case? If so, I've read old blog posts about… --- ## [Dr Racket stepper from the interactions area](https://racket.discourse.group/t/dr-racket-stepper-from-the-interactions-area/1396)
**Author:** [@jgomo3](https://racket.discourse.group/u/jgomo3)\ **Replies:** 5\ **Last updated:** [October 20, 2022, 9:23pm UTC](https://racket.discourse.group/t/dr-racket-stepper-from-the-interactions-area/1396 "2022-10-20T21:23:25Z")
Using BSL, Is it possible to run the stepper from the interaction area? So instead of evaluating the expression directly, DrRacket launch the Stepper just for that expression written in the prompt? The idea is to "run"… --- ## [Multiple bibliographies in a scribble document](https://racket.discourse.group/t/multiple-bibliographies-in-a-scribble-document/1373)
**Author:** [@brittAnderson](https://racket.discourse.group/u/brittAnderson)\ **Replies:** 2\ **Last updated:** [October 16, 2022, 1:10pm UTC](https://racket.discourse.group/t/multiple-bibliographies-in-a-scribble-document/1373 "2022-10-16T13:10:35Z")
I am writing a scribble document for a class I am teaching and am including references. The document is rather long and I would like the references to appear in the sections where they are referred to. Thus there will be… --- ## [When might \`(find-lib-dir)\` return \`#f\`?](https://racket.discourse.group/t/when-might-find-lib-dir-return-f/1377)
**Author:** [@LiberalArtist](https://racket.discourse.group/u/LiberalArtist)\ **Replies:** 1\ **Last updated:** [October 14, 2022, 10:42pm UTC](https://racket.discourse.group/t/when-might-find-lib-dir-return-f/1377 "2022-10-14T22:42:54Z")
Functions like find-lib-dir from setup/dirs document that: The result is #f if no such directory is available. What does "available" mean in this context? From experiments, it seems that the functions don't return #f … --- ## [Is there a PB decompiler?](https://racket.discourse.group/t/is-there-a-pb-decompiler/1381)
**Author:** [@jbclements](https://racket.discourse.group/u/jbclements)\ **Replies:** 1\ **Last updated:** [October 14, 2022, 10:25pm UTC](https://racket.discourse.group/t/is-there-a-pb-decompiler/1381 "2022-10-14T22:25:55Z")
I'm hoping this doesn't have an obvious documented answer: is there a way to decompile PB (portable bytecode) files? I see that the pb implementation went in around 2020, with substantial additions earlier this year in o… --- ## [Plotting a lambda that returns a (math/matrix) vector](https://racket.discourse.group/t/plotting-a-lambda-that-returns-a-math-matrix-vector/1365)
**Author:** [@GregVernon](https://racket.discourse.group/u/GregVernon)\ **Replies:** 3\ **Last updated:** [October 11, 2022, 4:20pm UTC](https://racket.discourse.group/t/plotting-a-lambda-that-returns-a-math-matrix-vector/1365 "2022-10-11T16:20:13Z")
I'm writing a text where I'm needing to plot polynomial bases and operations on them. The bases are often represented in a vector form, e.g., \\mathbf{N}^p(\\xi) = \[ N\_0^p(\\xi), N\_1^p(\\xi), \\dots, N\_p^p(\\xi) \]^T Where… --- ## [How to use \`head-extra\` in scribble?](https://racket.discourse.group/t/how-to-use-head-extra-in-scribble/1371)
**Author:** [@KDr2](https://racket.discourse.group/u/KDr2)\ **Replies:** 6\ **Last updated:** [October 11, 2022, 12:35pm UTC](https://racket.discourse.group/t/how-to-use-head-extra-in-scribble/1371 "2022-10-11T12:35:28Z")
I want to add a favicon to my website which is built with scribble, but when I put something like (make-head-extra ...) into my scribble file, it tells me that: not valid in document body (need a pre-part for decode) i… --- ## [Does Racket run on Windows 7?](https://racket.discourse.group/t/does-racket-run-on-windows-7/1351)
**Author:** [@alexh](https://racket.discourse.group/u/alexh)\ **Replies:** 4\ **Last updated:** [October 10, 2022, 3:52pm UTC](https://racket.discourse.group/t/does-racket-run-on-windows-7/1351 "2022-10-10T15:52:45Z")
A user of ActivityLog2 reported that the application fails to run on Window7, and the application is built using Racket 8.6 CS. Since the application itself does not load additional DLLs except for what Racket librarie… --- ## [FFI: Converting from \_pointer to byte string](https://racket.discourse.group/t/ffi-converting-from-pointer-to-byte-string/1349)
**Author:** [@jA\_cOp](https://racket.discourse.group/u/jA_cOp)\ **Replies:** 8\ **Last updated:** [October 6, 2022, 12:59pm UTC](https://racket.discourse.group/t/ffi-converting-from-pointer-to-byte-string/1349 "2022-10-06T12:59:23Z")
I have a C struct like so: (define-cstruct \_foo (\[data \_pointer\] \[len \_int32\])) I then get an instance of this struct as an output parameter of a C function. data points to a non-null-terminated array of bytes, of leng… --- ## [Scribble: How to wrap a subsection in a custom \`div\` element?](https://racket.discourse.group/t/scribble-how-to-wrap-a-subsection-in-a-custom-div-element/1340)
**Author:** [@sschwarzer](https://racket.discourse.group/u/sschwarzer)\ **Replies:** 5\ **Last updated:** [October 6, 2022, 12:06pm UTC](https://racket.discourse.group/t/scribble-how-to-wrap-a-subsection-in-a-custom-div-element/1340 "2022-10-06T12:06:22Z")
I'm trying to write a function that wraps a subsection, i.e. the subsection and the content belonging to the subsection, in a div element with a custom class. The function without the div wrapping currently looks like t… --- ## [Package dependency cycles](https://racket.discourse.group/t/package-dependency-cycles/1353)
**Author:** [@LiberalArtist](https://racket.discourse.group/u/LiberalArtist)\ **Replies:** 1\ **Last updated:** [October 6, 2022, 3:51am UTC](https://racket.discourse.group/t/package-dependency-cycles/1353 "2022-10-06T03:51:59Z")
While working on support for Racket packages in Guix, I learned that packages can have cyclic dependencies. Cycles seem rare, but, since one cycle involves base and racket-lib, they have to be accounted for from the begi… --- ## [2htdp save-movie analog of save-image?](https://racket.discourse.group/t/2htdp-save-movie-analog-of-save-image/1352)
**Author:** [@jasonhemann](https://racket.discourse.group/u/jasonhemann)\ **Replies:** 2\ **Last updated:** [October 5, 2022, 7:48pm UTC](https://racket.discourse.group/t/2htdp-save-movie-analog-of-save-image/1352 "2022-10-05T19:48:37Z")
2htdp/image includes save-image, a built-in way to easily export an image to disk. Is there a comparably easy way to save a movie that you'd produce with the run-movie function? --- ## [How to use the profiler?](https://racket.discourse.group/t/how-to-use-the-profiler/1345)
**Author:** [@dstorrs](https://racket.discourse.group/u/dstorrs)\ **Replies:** 4\ **Last updated:** [October 4, 2022, 8:35pm UTC](https://racket.discourse.group/t/how-to-use-the-profiler/1345 "2022-10-04T20:35:29Z")
I'm looking at the docs on the profiler and having some trouble. What I see is the following: profile will accept some expressions, run them, gather timing data, analyze it, and render it. It's a macro wrapper around… --- ## [How to get handin to work with 2htdp/image?](https://racket.discourse.group/t/how-to-get-handin-to-work-with-2htdp-image/1333)
**Author:** [@jestarray](https://racket.discourse.group/u/jestarray)\ **Replies:** 2\ **Last updated:** [September 28, 2022, 5:42pm UTC](https://racket.discourse.group/t/how-to-get-handin-to-work-with-2htdp-image/1333 "2022-09-28T17:42:16Z")
; problem1.rkt (require 2htdp/image) (check-expect (myadd1 1) 2) (define (myadd1 n) (+ n 1)) ; checker.rkt (check: :language '(special intermediate) :requires '(2htdp/image 2htdp/universe)) ; I get this e… --- ## [Elemtag and elemref advice for Scribble documents](https://racket.discourse.group/t/elemtag-and-elemref-advice-for-scribble-documents/1329)
**Author:** [@brittAnderson](https://racket.discourse.group/u/brittAnderson)\ **Replies:** 2\ **Last updated:** [September 27, 2022, 11:29am UTC](https://racket.discourse.group/t/elemtag-and-elemref-advice-for-scribble-documents/1329 "2022-09-27T11:29:56Z")
I am trying to figure out if I can use, and how to use, elemtag and elemref to create hyperlinks to equations. I would like to do something like: @elemtag{eqn1 @($$ "1 + 1 = 2")} and later be able to create a link with… --- ## [How to prevent Compiled Racket GUI program opening a black terminal window?](https://racket.discourse.group/t/how-to-prevent-compiled-racket-gui-program-opening-a-black-terminal-window/1320)
**Author:** [@hrvoje064](https://racket.discourse.group/u/hrvoje064)\ **Replies:** 11\ **Last updated:** [September 24, 2022, 6:25am UTC](https://racket.discourse.group/t/how-to-prevent-compiled-racket-gui-program-opening-a-black-terminal-window/1320 "2022-09-24T06:25:57Z")
I find this problem very strange because it does not behave the same on all OS that I tested. The problem is following (actually not really a problem, just annoyance): I compile #lang racket/gui source file with follow… --- ## [(expt 2 #large) gives different results/aborts](https://racket.discourse.group/t/expt-2-large-gives-different-results-aborts/1325)
**Author:** [@Dominique](https://racket.discourse.group/u/Dominique)\ **Replies:** 1\ **Last updated:** [September 23, 2022, 7:44pm UTC](https://racket.discourse.group/t/expt-2-large-gives-different-results-aborts/1325 "2022-09-23T19:44:56Z")
Hi newbie here, I was playing around with racket and tried: (Every next large number has the last digit removed from the previous one) (expt 2 1234567890123456789) ash: out of memory \[,bt for context\] then \> (exp… [Previous page](https://racket.discourse.group/c/questions/6.md?page=23) [Next page](https://racket.discourse.group/c/questions/6.md?page=25)