# Questions & Answers **URL:** https://racket.discourse.group/c/questions/6.md?page=31 [Latest](https://racket.discourse.group/latest.md) · [Categories](https://racket.discourse.group/categories.md) · [Tags](https://racket.discourse.group/tags.md) **Page:** 32 --- ## [Default .gitignore for Racket](https://racket.discourse.group/t/default-gitignore-for-racket/534)
**Author:** [@soegaard](https://racket.discourse.group/u/soegaard)\ **Replies:** 28\ **Last updated:** [February 22, 2022, 1:23pm UTC](https://racket.discourse.group/t/default-gitignore-for-racket/534 "2022-02-22T13:23:31Z")
The git command uses the file .gitignore to learn about files whose changes doesn't matter. Do you have one to share? Also, anyone up for the challenge of adding a default one for Racket on Github? --- ## [Filesystem-change-evt triggers twice](https://racket.discourse.group/t/filesystem-change-evt-triggers-twice/709)
**Author:** [@dstorrs](https://racket.discourse.group/u/dstorrs)\ **Replies:** 2\ **Last updated:** [February 19, 2022, 5:06pm UTC](https://racket.discourse.group/t/filesystem-change-evt-triggers-twice/709 "2022-02-19T17:06:02Z")
\#lang racket (require racket/runtime-path) (define-runtime-path here ".") (define the-path (build-path here "touchme.txt")) (let loop () (displayln "starting the loop...") (sync (filesystem-change-evt the-path)) … --- ## [How ellipsis works in macro?](https://racket.discourse.group/t/how-ellipsis-works-in-macro/692)
**Author:** [@chansey97](https://racket.discourse.group/u/chansey97)\ **Replies:** 7\ **Last updated:** [February 19, 2022, 6:50am UTC](https://racket.discourse.group/t/how-ellipsis-works-in-macro/692 "2022-02-19T06:50:58Z")
The ellipsis seems to work in the most obvious way, but it is still difficult to understand for me. Below I will explain my current understanding and provide a naive translation to map, but there are quite a few examples… --- ## [How can i use sets methods to sort sets and create sequences?](https://racket.discourse.group/t/how-can-i-use-sets-methods-to-sort-sets-and-create-sequences/708)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 2\ **Last updated:** [February 18, 2022, 9:09pm UTC](https://racket.discourse.group/t/how-can-i-use-sets-methods-to-sort-sets-and-create-sequences/708 "2022-02-18T21:09:00Z")
I am asking this question as i am struggling to use sets and i would like to better understand how to tackle this goal .My goal here is to to write a function which sorts the union of all my three sets in alphabetical … --- ## [Get to type (apply in-parallel lst)](https://racket.discourse.group/t/get-to-type-apply-in-parallel-lst/683)
**Author:** [@scolobb](https://racket.discourse.group/u/scolobb)\ **Replies:** 5\ **Last updated:** [February 18, 2022, 2:53pm UTC](https://racket.discourse.group/t/get-to-type-apply-in-parallel-lst/683 "2022-02-18T14:53:04Z")
Hi, I am trying to type the following function: (: lists-transpose (All (a) (-\> (Listof (Listof a)) (Listof (Listof a))))) (define (lists-transpose lsts) (sequence-\>list (in-values-sequence (apply in-parallel lst))))… --- ## [When to use Typed Racket vs Contracts](https://racket.discourse.group/t/when-to-use-typed-racket-vs-contracts/691)
**Author:** [@Decabytes](https://racket.discourse.group/u/Decabytes)\ **Replies:** 6\ **Last updated:** [February 18, 2022, 2:38pm UTC](https://racket.discourse.group/t/when-to-use-typed-racket-vs-contracts/691 "2022-02-18T14:38:07Z")
I’m currently using the Racket wrapped library for C library Raylib and one problem that I’m running into is that when I pass the wrong types to a function the whole program crashes. I’ve never used them before, but it s… --- ## [Tips for building native libraries for Racket?](https://racket.discourse.group/t/tips-for-building-native-libraries-for-racket/706)
**Author:** [@simonls](https://racket.discourse.group/u/simonls)\ **Replies:** 5\ **Last updated:** [February 18, 2022, 3:40am UTC](https://racket.discourse.group/t/tips-for-building-native-libraries-for-racket/706 "2022-02-18T03:40:40Z")
In this thread I have described how I solved my problem (ffi bindings are difficult to create) by creating a wrapper library around freetype (simpler to create ffi bindings): But to be silly and quote myself: So this… --- ## [FFI define-cstruct recursive dependencies on types](https://racket.discourse.group/t/ffi-define-cstruct-recursive-dependencies-on-types/353)
**Author:** [@simonls](https://racket.discourse.group/u/simonls)\ **Replies:** 4\ **Last updated:** [February 17, 2022, 10:24pm UTC](https://racket.discourse.group/t/ffi-define-cstruct-recursive-dependencies-on-types/353 "2022-02-17T22:24:48Z")
I am trying to use define-cstruct 1.4 C Structs to define many cstructs some of those have pointers to other cstructs. My actual code is quite big, but I think it boils down to being able to define mutually recursive cst… --- ## [How-do-i-show-results-of-two-functions-in-another-function](https://racket.discourse.group/t/how-do-i-show-results-of-two-functions-in-another-function/705)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 1\ **Last updated:** [February 17, 2022, 12:58am UTC](https://racket.discourse.group/t/how-do-i-show-results-of-two-functions-in-another-function/705 "2022-02-17T00:58:25Z")
I have been as a part of a school assignment been coding a program on racket,which is similar to the tfl route planner. My objective is to create a function which takes the results from the two functions, for example for… --- ## [Need help using set-union](https://racket.discourse.group/t/need-help-using-set-union/703)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 4\ **Last updated:** [February 16, 2022, 7:43pm UTC](https://racket.discourse.group/t/need-help-using-set-union/703 "2022-02-16T19:43:56Z")
i have written this code which basically checks if the user has submitted and empty input (which returns and error) or inputs a letter which does not belong in neither of three sets,and if its successful it will return… --- ## [Define-attributes macro, is this useful, ideas for improvements?](https://racket.discourse.group/t/define-attributes-macro-is-this-useful-ideas-for-improvements/300)
**Author:** [@simonls](https://racket.discourse.group/u/simonls)\ **Replies:** 9\ **Last updated:** [February 16, 2022, 5:22pm UTC](https://racket.discourse.group/t/define-attributes-macro-is-this-useful-ideas-for-improvements/300 "2022-02-16T17:22:08Z")
I had a define-attributes macro for a while now in a project, I don't use it a whole lot, but where I do it seems to make the code less verbose. But I think my understanding of source locations is still not the best so t… --- ## [\`raco pkg new\` License not recognized by github](https://racket.discourse.group/t/raco-pkg-new-license-not-recognized-by-github/700)
**Author:** [@simonls](https://racket.discourse.group/u/simonls)\ **Replies:** 0\ **Last updated:** [February 16, 2022, 6:15am UTC](https://racket.discourse.group/t/raco-pkg-new-license-not-recognized-by-github/700 "2022-02-16T06:15:07Z")
This is the first time I have used the raco pkg new command to create my new package. (before I created them manually) I noticed that for my manually created packages the license is recognized by github and shown with a… --- ## [Is rainbow-delimiters-mode possible in DrRacket? ](https://racket.discourse.group/t/is-rainbow-delimiters-mode-possible-in-drracket/697)
**Author:** [@jolyon](https://racket.discourse.group/u/jolyon)\ **Replies:** 4\ **Last updated:** [February 15, 2022, 11:11pm UTC](https://racket.discourse.group/t/is-rainbow-delimiters-mode-possible-in-drracket/697 "2022-02-15T23:11:10Z")
Forgive a possibly newbish question; I have just discovered drracket, and am loving it! One thing I am missing from emacs a lot is rainbow-delimiters-mode. Is there a way to simulate this in drracket? This would make … --- ## ["libintl.9.dylib cannot be verified" error with MacOS executable](https://racket.discourse.group/t/libintl-9-dylib-cannot-be-verified-error-with-macos-executable/690)
**Author:** [@jjsimpso](https://racket.discourse.group/u/jjsimpso)\ **Replies:** 2\ **Last updated:** [February 15, 2022, 12:19am UTC](https://racket.discourse.group/t/libintl-9-dylib-cannot-be-verified-error-with-macos-executable/690 "2022-02-15T00:19:29Z")
I have an application that I am cross-compiling binaries for. The MacOS binary is giving this error: Full details at macOS suspicious of libintl.9.dylib · Issue #2 · jjsimpso/molasses · GitHub. I cross compiled this … --- ## [Using \`draw-bitmap\` and \`draw-bitmap-section\` with transparent color images](https://racket.discourse.group/t/using-draw-bitmap-and-draw-bitmap-section-with-transparent-color-images/694)
**Author:** [@soegaard](https://racket.discourse.group/u/soegaard)\ **Replies:** 2\ **Last updated:** [February 14, 2022, 3:06pm UTC](https://racket.discourse.group/t/using-draw-bitmap-and-draw-bitmap-section-with-transparent-color-images/694 "2022-02-14T15:06:40Z")
Hi All, I need help to draw a "sprite" (small bitmap) on top of a bitmap. The sprite in question is consists of a transparent background and has a solid yellow circle in the center. My test program looks like this (sc… --- ## [A question about free-identifier=?](https://racket.discourse.group/t/a-question-about-free-identifier/685)
**Author:** [@chansey97](https://racket.discourse.group/u/chansey97)\ **Replies:** 5\ **Last updated:** [February 13, 2022, 11:28pm UTC](https://racket.discourse.group/t/a-question-about-free-identifier/685 "2022-02-13T23:28:39Z")
I am learning Racket macro. I have a question about free-identifier=?. Why the following code return #t? (free-identifier=? #'car (let (\[car 8\]) #'car)) ;; #t Does the #'car under the let access the same binding? Th… --- ## [Syntax-case, require, file](https://racket.discourse.group/t/syntax-case-require-file/687)
**Author:** [@Kalimehtar](https://racket.discourse.group/u/Kalimehtar)\ **Replies:** 4\ **Last updated:** [February 13, 2022, 3:16pm UTC](https://racket.discourse.group/t/syntax-case-require-file/687 "2022-02-13T15:16:35Z")
Why (define-syntax (require-file stx) (syntax-case stx () \[(\_ x) #'(require (file x))\])) doesn't work (it compiles, but doesn't import identifiers)? (define-syntax (require-file\* stx) (syntax-case stx () … --- ## [Suggestion: track if your modules have been installed from pkg server](https://racket.discourse.group/t/suggestion-track-if-your-modules-have-been-installed-from-pkg-server/675)
**Author:** [@dstorrs](https://racket.discourse.group/u/dstorrs)\ **Replies:** 3\ **Last updated:** [February 12, 2022, 12:10am UTC](https://racket.discourse.group/t/suggestion-track-if-your-modules-have-been-installed-from-pkg-server/675 "2022-02-12T00:10:28Z")
I often find myself wondering if the packages I've posted are in use by anyone. In part for the egoboo but also because if they aren't in use by anyone else then backwards compatibility isn't as important a consideratio… --- ## [How to package non-racket files into racket binary](https://racket.discourse.group/t/how-to-package-non-racket-files-into-racket-binary/667)
**Author:** [@dannypsnl](https://racket.discourse.group/u/dannypsnl)\ **Replies:** 7\ **Last updated:** [February 11, 2022, 5:26pm UTC](https://racket.discourse.group/t/how-to-package-non-racket-files-into-racket-binary/667 "2022-02-11T17:26:08Z")
The problem I actually facing is I write a compiler in Racket but the runtime is written in C, I write (parameterize (\[current-directory "./runtime"\]) (match-define (list stdout stdin status stderr do) (proces… --- ## [Some questions about stateless web-server](https://racket.discourse.group/t/some-questions-about-stateless-web-server/678)
**Author:** [@Hanson](https://racket.discourse.group/u/Hanson)\ **Replies:** 2\ **Last updated:** [February 11, 2022, 2:36pm UTC](https://racket.discourse.group/t/some-questions-about-stateless-web-server/678 "2022-02-11T14:36:08Z")
I am really confused about the stateless web-server. What's the diffrence between a (serve/servlet start #:stateless? #t) and a (require web-server) version of stateless server? With a stateful server, the url has … --- ## [Does custodian-shutdown-all block until threads are suspended/killed?](https://racket.discourse.group/t/does-custodian-shutdown-all-block-until-threads-are-suspended-killed/663)
**Author:** [@jjsimpso](https://racket.discourse.group/u/jjsimpso)\ **Replies:** 6\ **Last updated:** [February 8, 2022, 10:01pm UTC](https://racket.discourse.group/t/does-custodian-shutdown-all-block-until-threads-are-suspended-killed/663 "2022-02-08T22:01:13Z")
I have some code that is using custodian-shutdown-all in order to cancel an operation running in a previously spawned thread. I had made the assumption that custodian-shutdown-all would not return until the thread(s) it… --- ## [Question: namespace-require](https://racket.discourse.group/t/question-namespace-require/669)
**Author:** [@joskoot](https://racket.discourse.group/u/joskoot)\ **Replies:** 3\ **Last updated:** [February 8, 2022, 10:22am UTC](https://racket.discourse.group/t/question-namespace-require/669 "2022-02-08T10:22:11Z")
Hi This works: (let ((ns (make-base-namespace))) (parameterize ((current-namespace ns)) (namespace-require '(file "tests.rkt")))) This does not: (let ((ns (make-base-namespace))) (namespace-require '(file "tests.… --- ## [How to use mandatory arguments on the command line](https://racket.discourse.group/t/how-to-use-mandatory-arguments-on-the-command-line/655)
**Author:** [@dstorrs](https://racket.discourse.group/u/dstorrs)\ **Replies:** 7\ **Last updated:** [February 7, 2022, 4:30pm UTC](https://racket.discourse.group/t/how-to-use-mandatory-arguments-on-the-command-line/655 "2022-02-07T16:30:57Z")
I'm refreshing on 15.9 Command-Line Parsing and I note that there doesn't seem to be a way to say "this flag must be present." Am I missing something? Here's the normal workaround: #lang racket (define name (make-par… --- ## [Permission problem for scribble documentation when updating racket version on Ubuntu](https://racket.discourse.group/t/permission-problem-for-scribble-documentation-when-updating-racket-version-on-ubuntu/666)
**Author:** [@marc](https://racket.discourse.group/u/marc)\ **Replies:** 0\ **Last updated:** [February 7, 2022, 8:14am UTC](https://racket.discourse.group/t/permission-problem-for-scribble-documentation-when-updating-racket-version-on-ubuntu/666 "2022-02-07T08:14:47Z")
I have updated my version of Racket from 8.2 to 8.3 on Ubuntu 20.4 (Focal). While it works successfully, when I install new packages, I get the following error: open-output-file: error opening file path: /usr/share/ra… --- ## [Building with \`--enable-scheme\`](https://racket.discourse.group/t/building-with-enable-scheme/664)
**Author:** [@LiberalArtist](https://racket.discourse.group/u/LiberalArtist)\ **Replies:** 5\ **Last updated:** [February 7, 2022, 6:48am UTC](https://racket.discourse.group/t/building-with-enable-scheme/664 "2022-02-07T06:48:25Z")
I know how to build Racket from source and then use the copy of Chez Scheme built as part of the process, as discussed in Running chez after building Racket?. My case (as part of working on the Guix packaging of Racket) … --- ## [Question on new Racket install graphic IDE](https://racket.discourse.group/t/question-on-new-racket-install-graphic-ide/657)
**Author:** [@joekillian](https://racket.discourse.group/u/joekillian)\ **Replies:** 9\ **Last updated:** [February 5, 2022, 6:12pm UTC](https://racket.discourse.group/t/question-on-new-racket-install-graphic-ide/657 "2022-02-05T18:12:04Z")
Why in the code below getting "read-syntax: #lang not enabled" In the graphic IDE I get: "Welcome to DrRacket, version 8.3 \[cs\]. Language: Advanced Student; memory limit: 128 MB. read-syntax: #lang not enabled possi… --- ## [I think "state" of big-bang in 2htdp/universe does not work properly](https://racket.discourse.group/t/i-think-state-of-big-bang-in-2htdp-universe-does-not-work-properly/653)
**Author:** [@cametan](https://racket.discourse.group/u/cametan)\ **Replies:** 8\ **Last updated:** [February 5, 2022, 4:56pm UTC](https://racket.discourse.group/t/i-think-state-of-big-bang-in-2htdp-universe-does-not-work-properly/653 "2022-02-05T16:56:40Z")
I think "state" of big-bang in 2htdp/universe does not work properly. It seems the world struct should be widened to show its properties, or slots; however the size changer does not work at all on Linux version; there… --- ## [List of figures in scribble document](https://racket.discourse.group/t/list-of-figures-in-scribble-document/654)
**Author:** [@dominik.pantucek](https://racket.discourse.group/u/dominik.pantucek)\ **Replies:** 0\ **Last updated:** [February 4, 2022, 7:07pm UTC](https://racket.discourse.group/t/list-of-figures-in-scribble-document/654 "2022-02-04T19:07:26Z")
It is possible to use figures\[1\] from extra scribble libraries to show and reference figures within a scribble document. But I found no way of creating LaTeX-like list of figures. Something similar to table-of-contents\[2… --- ## [Vectors, boxes and places](https://racket.discourse.group/t/vectors-boxes-and-places/648)
**Author:** [@timjervis](https://racket.discourse.group/u/timjervis)\ **Replies:** 1\ **Last updated:** [February 4, 2022, 2:26pm UTC](https://racket.discourse.group/t/vectors-boxes-and-places/648 "2022-02-04T14:26:02Z")
Dear Racketeers, Is there something I have misunderstood about vectors, boxes and places which might explain why immutable boxes are not place-message-allowed, but immutable vectors are? \> (place-message-allowed? (box-… --- ## [How to find the definition of functions?](https://racket.discourse.group/t/how-to-find-the-definition-of-functions/645)
**Author:** [@yuzeng](https://racket.discourse.group/u/yuzeng)\ **Replies:** 3\ **Last updated:** [February 3, 2022, 8:29pm UTC](https://racket.discourse.group/t/how-to-find-the-definition-of-functions/645 "2022-02-03T20:29:44Z")
Hi, I am a rookie to Racket. Recently I am debugging a Racket program, which depends on several other packages. I found it difficult to locate the definition for each function. The only way I know is using "trace". But t… [Previous page](https://racket.discourse.group/c/questions/6.md?page=30) [Next page](https://racket.discourse.group/c/questions/6.md?page=32)