# Questions & Answers **URL:** https://racket.discourse.group/c/questions/6.md?page=29 [Latest](https://racket.discourse.group/latest.md) · [Categories](https://racket.discourse.group/categories.md) · [Tags](https://racket.discourse.group/tags.md) **Page:** 30 --- ## [\`raco pkg migrate\` for \`--link\` and \`--no-setup\` packages](https://racket.discourse.group/t/raco-pkg-migrate-for-link-and-no-setup-packages/926)
**Author:** [@greghendershott](https://racket.discourse.group/u/greghendershott)\ **Replies:** 3\ **Last updated:** [April 26, 2022, 4:48pm UTC](https://racket.discourse.group/t/raco-pkg-migrate-for-link-and-no-setup-packages/926 "2022-04-26T16:48:34Z")
How does raco pkg migrate handle linked packages (those originally installed with --link from a directory package source)? Does it: Copy (ala --copy), such that the original's compiled remains in the original link s… --- ## [How to run interactively from terminal?](https://racket.discourse.group/t/how-to-run-interactively-from-terminal/918)
**Author:** [@jkleiser](https://racket.discourse.group/u/jkleiser)\ **Replies:** 7\ **Last updated:** [April 26, 2022, 8:49am UTC](https://racket.discourse.group/t/how-to-run-interactively-from-terminal/918 "2022-04-26T08:49:26Z")
In my code I have a function that I would like to call while in the REPL in my macOS Terminal. I start my code like this: racket -i my-code.rkt However, if I try to execute my function, doing (my-fun), I get this error … --- ## [Is it possible to use "s-exp" reader to parse expressions without parens wrapped?](https://racket.discourse.group/t/is-it-possible-to-use-s-exp-reader-to-parse-expressions-without-parens-wrapped/924)
**Author:** [@doublex](https://racket.discourse.group/u/doublex)\ **Replies:** 4\ **Last updated:** [April 25, 2022, 8:28pm UTC](https://racket.discourse.group/t/is-it-possible-to-use-s-exp-reader-to-parse-expressions-without-parens-wrapped/924 "2022-04-25T20:28:19Z")
Hi, I'm trying to implement a typed language using Racket's LOP. since my calculus requires full annotation, it will be ugly to write code like (λ (x : t1) e t2) It becomes worser when lambda expression are nested lik… --- ## [Shared data structures between parallel workers in racket?](https://racket.discourse.group/t/shared-data-structures-between-parallel-workers-in-racket/909)
**Author:** [@yak](https://racket.discourse.group/u/yak)\ **Replies:** 11\ **Last updated:** [April 24, 2022, 1:04am UTC](https://racket.discourse.group/t/shared-data-structures-between-parallel-workers-in-racket/909 "2022-04-24T01:04:49Z")
We are working on parallelizing a long computation in racket so that it can take advantage of multiple cores while sharing data structures, and are hoping for some advice from the community. The computation consists of … --- ## [Reusable tests, test-cases, and test-suites](https://racket.discourse.group/t/reusable-tests-test-cases-and-test-suites/884)
**Author:** [@dominik.pantucek](https://racket.discourse.group/u/dominik.pantucek)\ **Replies:** 4\ **Last updated:** [April 23, 2022, 11:00am UTC](https://racket.discourse.group/t/reusable-tests-test-cases-and-test-suites/884 "2022-04-23T11:00:35Z")
Hello fellow Racketeers, while preparing some lecture notes I noticed that sometimes it is useful to have a multiple implementations of single algorithm prepared. As I am playing with this idea, I started to write ident… --- ## [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… --- ## [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… --- ## [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… --- ## [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 … --- ## [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… --- ## [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… --- ## [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… --- ## [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.… --- ## [Passing procedures of unknow arity across typed/untyped boundary](https://racket.discourse.group/t/passing-procedures-of-unknow-arity-across-typed-untyped-boundary/831)
**Author:** [@scolobb](https://racket.discourse.group/u/scolobb)\ **Replies:** 9\ **Last updated:** [April 2, 2022, 9:41am UTC](https://racket.discourse.group/t/passing-procedures-of-unknow-arity-across-typed-untyped-boundary/831 "2022-04-02T09:41:21Z")
Hello, I need to pass a function of unknown arity to another function in Typed Racket, in particular because the approach using polymorphic functions from this thread does not completely fit my use case, and also becaus… --- ## [\#lang plai-typed not available?](https://racket.discourse.group/t/lang-plai-typed-not-available/840)
**Author:** [@AlexG](https://racket.discourse.group/u/AlexG)\ **Replies:** 2\ **Last updated:** [April 2, 2022, 1:51am UTC](https://racket.discourse.group/t/lang-plai-typed-not-available/840 "2022-04-02T01:51:37Z")
Hello, first post here: I want to work through Shriram Krishnamurthi's PLAI book, but the language specified (#lang plai-typed) does not appear to be included in my Dr.Racket 8.4 Ubuntu distribution. Is there a way to … --- ## [Parsing X.509 certificates](https://racket.discourse.group/t/parsing-x-509-certificates/833)
**Author:** [@dominik.pantucek](https://racket.discourse.group/u/dominik.pantucek)\ **Replies:** 4\ **Last updated:** [March 29, 2022, 3:36am UTC](https://racket.discourse.group/t/parsing-x-509-certificates/833 "2022-03-29T03:36:51Z")
Long, long time ago, someone implemented a very simple batch request/response processing with signature verification, using openssl\_verify\[1\]. Yes, PHP. Now we are re-implementing the receiver part in Racket. Trouble i… --- ## [Uni-table formatting help](https://racket.discourse.group/t/uni-table-formatting-help/823)
**Author:** [@rscho](https://racket.discourse.group/u/rscho)\ **Replies:** 6\ **Last updated:** [March 28, 2022, 7:09pm UTC](https://racket.discourse.group/t/uni-table-formatting-help/823 "2022-03-28T19:09:47Z")
Hi, I am having a go at the uni-table package (hi @dominik.pantucek! :slight\_smile: ). This styling: (uni-table-\>string tbl #:table-border '(solid light) #:col-borders '((solid lef… --- ## [How can i create function that takes an instance and updates it?](https://racket.discourse.group/t/how-can-i-create-function-that-takes-an-instance-and-updates-it/820)
**Author:** [@osman44](https://racket.discourse.group/u/osman44)\ **Replies:** 3\ **Last updated:** [March 25, 2022, 4:59pm UTC](https://racket.discourse.group/t/how-can-i-create-function-that-takes-an-instance-and-updates-it/820 "2022-03-25T16:59:18Z")
i am trying to complete a homework task based on structure,but when i came to the third bullet point where it asked me to create a function for a customer instance,i got confused how am i supposed to do that,because i do… --- ## [What are examples of use-cases for continuations?](https://racket.discourse.group/t/what-are-examples-of-use-cases-for-continuations/806)
**Author:** [@jcottrell](https://racket.discourse.group/u/jcottrell)\ **Replies:** 13\ **Last updated:** [March 24, 2022, 8:39pm UTC](https://racket.discourse.group/t/what-are-examples-of-use-cases-for-continuations/806 "2022-03-24T20:39:40Z")
I read the recent reddit question about finding the first odd number. I was going to respond with my meager knowledge about continuations that I'm trying to accumulate as I go through The Seasoned Schemer but first I tho… [Previous page](https://racket.discourse.group/c/questions/6.md?page=28) [Next page](https://racket.discourse.group/c/questions/6.md?page=30)