# Latest **URL:** https://racket.discourse.group/latest.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 --- ## [Rewind a port (file) or other method?](https://racket.discourse.group/t/rewind-a-port-file-or-other-method/2837)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 6\ **Last updated:** [March 26, 2024, 10:36pm UTC](https://racket.discourse.group/t/rewind-a-port-file-or-other-method/2837 "2024-03-26T22:36:35Z")
hello, i just want to skip comments and blank lines at the beginning of a file, i find a solution that rewind the port/file using file-position but is there other method/solution? (require (only-in racket/base \[do d… --- ## [Pattern matching 'Some' and 'None'](https://racket.discourse.group/t/pattern-matching-some-and-none/2819)
**Author:** [@mohanr](https://racket.discourse.group/u/mohanr)\ **Replies:** 3\ **Last updated:** [March 26, 2024, 5:28am UTC](https://racket.discourse.group/t/pattern-matching-some-and-none/2819 "2024-03-26T05:28:57Z")
Hi I am porting SML to Racket. Managed to create a recursive data type like this. I reuse a macro by Alexis King for this. (define-datatype Expr ( BoolValue Boolean ) ( IntValue Number ) ( Op Expr (U Plus GTE… --- ## [SRFI 48: is it possible to get rid of the decimal point?](https://racket.discourse.group/t/srfi-48-is-it-possible-to-get-rid-of-the-decimal-point/2836)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 4\ **Last updated:** [March 25, 2024, 6:32pm UTC](https://racket.discourse.group/t/srfi-48-is-it-possible-to-get-rid-of-the-decimal-point/2836 "2024-03-25T18:32:22Z")
Hi, I've got this: "helpers.rkt"\> (format "~0,0F" 1.22) "1." "helpers.rkt"\> (format "~0,0F" 1.55) "2." I'd be satisfied with the same without the decimal point. Is there a way? --- ## [FFMPEG Filtergraph Generator](https://racket.discourse.group/t/ffmpeg-filtergraph-generator/2831)
**Author:** [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Replies:** 2\ **Last updated:** [March 25, 2024, 3:50am UTC](https://racket.discourse.group/t/ffmpeg-filtergraph-generator/2831 "2024-03-25T03:50:31Z")
Hello, everyone! I have created an tiny ffmpeg (complex) filtergraph generator using a s-expression representation, which implements basic checks and character escaping. However, I find its syntax not very user-friendl… --- ## [NES emulator kind of working](https://racket.discourse.group/t/nes-emulator-kind-of-working/2830)
**Author:** [@default.kramer](https://racket.discourse.group/u/default.kramer)\ **Replies:** 1\ **Last updated:** [March 24, 2024, 6:05pm UTC](https://racket.discourse.group/t/nes-emulator-kind-of-working/2830 "2024-03-24T18:05:59Z")
It's still very rough in places, but my NES emulator is now functional enough to play some games. GitHub - default-kramer/nes-emu Choose the ROM you want to play by editing the rom-path in main.rkt, and then run raco ma… --- ## [A possible bug in the expander?](https://racket.discourse.group/t/a-possible-bug-in-the-expander/2829)
**Author:** [@dominik.pantucek](https://racket.discourse.group/u/dominik.pantucek)\ **Replies:** 0\ **Last updated:** [March 24, 2024, 9:31am UTC](https://racket.discourse.group/t/a-possible-bug-in-the-expander/2829 "2024-03-24T09:31:29Z")
Hello Racketeers, while working on new Actor Basic version I stumbled upon a strange behavior. I managed to narrow it down strictly to my rrll-abasic package (not in the package catalog) sources found at rrll-abasic · m… --- ## [Question about #lang reader](https://racket.discourse.group/t/question-about-lang-reader/2825)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 1\ **Last updated:** [March 24, 2024, 9:21am UTC](https://racket.discourse.group/t/question-about-lang-reader/2825 "2024-03-24T09:21:37Z")
hello, i try to add support for r6rs in my SRFI-105 reader, used this way: #lang reader "../src/SRFI-105.rkt" it used to return a module like this, reading an input file stream : (define (literal-read-syntax src in) … --- ## [Question about gensym](https://racket.discourse.group/t/question-about-gensym/2826)
**Author:** [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Replies:** 2\ **Last updated:** [March 23, 2024, 11:46am UTC](https://racket.discourse.group/t/question-about-gensym/2826 "2024-03-23T11:46:44Z")
Hello, everyone. I want to generate unique names containing only alphanumeric characters and '\_' in racket. Is it safe to use gensym? For example, (define (make-unique-name) (gensym 'my\_name)) Can I be sure (make-… --- ## [EBNF dialect used in the Racket docs](https://racket.discourse.group/t/ebnf-dialect-used-in-the-racket-docs/2821)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 6\ **Last updated:** [March 23, 2024, 6:09am UTC](https://racket.discourse.group/t/ebnf-dialect-used-in-the-racket-docs/2821 "2024-03-23T06:09:18Z")
Hi, Is there somewhere a description of the subj? --- ## [Local versus github links in scribble](https://racket.discourse.group/t/local-versus-github-links-in-scribble/2818)
**Author:** [@joskoot](https://racket.discourse.group/u/joskoot)\ **Replies:** 4\ **Last updated:** [March 22, 2024, 7:15pm UTC](https://racket.discourse.group/t/local-versus-github-links-in-scribble/2818 "2024-03-22T19:15:08Z")
local versus github links in scribble defmodule and hyperlinks act differently when installing from github or locally. I resolved the problem as follows: @(define-for-syntax local #f) @; set to #t when installing loca… --- ## [Hexadecimal notation in scribble interaction](https://racket.discourse.group/t/hexadecimal-notation-in-scribble-interaction/2816)
**Author:** [@joskoot](https://racket.discourse.group/u/joskoot)\ **Replies:** 1\ **Last updated:** [March 21, 2024, 4:10pm UTC](https://racket.discourse.group/t/hexadecimal-notation-in-scribble-interaction/2816 "2024-03-21T16:10:53Z")
\#lang scribble/manual @(require scribble/eval) @interaction\[(+ #xA #xA)\] Renders Is there a simple way to retain the hexadecimal notation? --- ## [Dealing with functions which may return values of different types](https://racket.discourse.group/t/dealing-with-functions-which-may-return-values-of-different-types/2815)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 5\ **Last updated:** [March 21, 2024, 10:58am UTC](https://racket.discourse.group/t/dealing-with-functions-which-may-return-values-of-different-types/2815 "2024-03-21T10:58:31Z")
Hi, I mean such functions like regexp-match. Here's a fragment of my code: ... (let (\[o-neal (regexp-match #px".\*?'(\[^'\]{1})" str)\]) (if (not (equal? o-neal #f)) (list-ref o-neal 0) ... It works, but I'd… --- ## [Typed Racket guidelines](https://racket.discourse.group/t/typed-racket-guidelines/2805)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 9\ **Last updated:** [March 20, 2024, 8:34pm UTC](https://racket.discourse.group/t/typed-racket-guidelines/2805 "2024-03-20T20:34:09Z")
Hi, Frankly, the question should be "Typed Racket: is it safe to use?". I sensibly asked the similar question about the Lazy Racket, and the unanimous answer was "forget it". Well, not exactly, but unless the general la… --- ## [How can I programmatically expand the "let" family of functions?](https://racket.discourse.group/t/how-can-i-programmatically-expand-the-let-family-of-functions/2811)
**Author:** [@JShoes1415](https://racket.discourse.group/u/JShoes1415)\ **Replies:** 11\ **Last updated:** [March 20, 2024, 6:29pm UTC](https://racket.discourse.group/t/how-can-i-programmatically-expand-the-let-family-of-functions/2811 "2024-03-20T18:29:21Z")
Hello! I am using Racket in a course at my university and I've found it quite enjoyable. I am working on an assignment where the use of let and let\* is limited so as to encourage good functional style. While I understan… --- ## [How to import a srfi in r6rs](https://racket.discourse.group/t/how-to-import-a-srfi-in-r6rs/2813)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 2\ **Last updated:** [March 20, 2024, 3:03pm UTC](https://racket.discourse.group/t/how-to-import-a-srfi-in-r6rs/2813 "2024-03-20T15:03:27Z")
hello, i try to import the SRFI 43 in a module and i want to do it the way r6rs allow it, i tried: #!r6rs (import (srfi (43)) (rnrs lists (6)) (rnrs base (6)) (rnrs io simple (6))) (display (find even? '(3 1 4 1 5… --- ## [Nested split-map-join, preferred style](https://racket.discourse.group/t/nested-split-map-join-preferred-style/2809)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 5\ **Last updated:** [March 20, 2024, 6:10am UTC](https://racket.discourse.group/t/nested-split-map-join-preferred-style/2809 "2024-03-20T06:10:05Z")
Hi, This is a small and clean example: a function to make a string of initials out of a string of \[co\]authors. Coauthors consist of a sequence of authors separated by comma Authors consist of a sequence of barrels (do… --- ## [Robocode Style Competitive Educational Game in Racket](https://racket.discourse.group/t/robocode-style-competitive-educational-game-in-racket/2808)
**Author:** [@markshead](https://racket.discourse.group/u/markshead)\ **Replies:** 4\ **Last updated:** [March 19, 2024, 10:30pm UTC](https://racket.discourse.group/t/robocode-style-competitive-educational-game-in-racket/2808 "2024-03-19T22:30:15Z")
Has anyone run across anything like https://robocode.sourceforge.io/ but in Racket? --- ## [Cannot modify a constant](https://racket.discourse.group/t/cannot-modify-a-constant/2802)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 2\ **Last updated:** [March 17, 2024, 11:24pm UTC](https://racket.discourse.group/t/cannot-modify-a-constant/2802 "2024-03-17T23:24:10Z")
hello, i find a little bug in one of my code. It is not easy to debug because it use a personal reader/parser,and a modified REPL for Racket . (based on this very interesting book: https://beautifulracket.com/) i have… --- ## [Idiomatic way of handling lists and/or tuples](https://racket.discourse.group/t/idiomatic-way-of-handling-lists-and-or-tuples/2800)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 6\ **Last updated:** [March 17, 2024, 6:42pm UTC](https://racket.discourse.group/t/idiomatic-way-of-handling-lists-and-or-tuples/2800 "2024-03-17T18:42:09Z")
Hi, Here's my unit test, or the first attempt at it: #lang racket/base (require rackunit "smallin.rkt") (define initials-block (list '("ron reagan-smith" "R.R-S.") '("Nell Guinn" "N.G.") '("ben lazar" "BL.… --- ## [Printf string representation as a list element](https://racket.discourse.group/t/printf-string-representation-as-a-list-element/2801)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 1\ **Last updated:** [March 17, 2024, 6:16pm UTC](https://racket.discourse.group/t/printf-string-representation-as-a-list-element/2801 "2024-03-17T18:16:11Z")
Hi, I can see this in REPL: "in-test.rkt"\> (define lst (list "alfa" 42)) "in-test.rkt"\> lst '("alfa" 42) "in-test.rkt"\> (printf "~a\\n" lst) (alfa 42) I should much prefer it being quoted in the last line. Is there a w… --- ## [Lazy Racket guidelines](https://racket.discourse.group/t/lazy-racket-guidelines/2792)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 3\ **Last updated:** [March 17, 2024, 4:07pm UTC](https://racket.discourse.group/t/lazy-racket-guidelines/2792 "2024-03-17T16:07:03Z")
Hi, I've seen just the docs, not much else on the Web. It says that I can use #lang lazy on per module basis. Does it mean that I can conveniently put all the laziness I need in my app in a separate file and get away wi… --- ## [DrRacket indentation issue](https://racket.discourse.group/t/drracket-indentation-issue/2777)
**Author:** [@matteo-daddio](https://racket.discourse.group/u/matteo-daddio)\ **Replies:** 5\ **Last updated:** [March 17, 2024, 3:45pm UTC](https://racket.discourse.group/t/drracket-indentation-issue/2777 "2024-03-17T15:45:10Z")
Hello, I've created an alias for lambda: (define-syntax procedure (syntax-rules () \[(procedure (arg ...) expr1 expr ...) (lambda (arg ...) expr1 expr ...)\])) but, when I use it, the indentation changes: (l… --- ## [Walking a file tree as a study in recursive generators](https://racket.discourse.group/t/walking-a-file-tree-as-a-study-in-recursive-generators/2787)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 14\ **Last updated:** [March 17, 2024, 10:38am UTC](https://racket.discourse.group/t/walking-a-file-tree-as-a-study-in-recursive-generators/2787 "2024-03-17T10:38:16Z")
Hi, I want to learn a Racket way of writing recursive generators. Speaking of the programming languages in general, it's either yield or flatMap approach, depending on the language. Walking the file tree, MWE, Python: … --- ## [: \`read' access denied for](https://racket.discourse.group/t/read-access-denied-for/1834)
**Author:** [@bsassoli](https://racket.discourse.group/u/bsassoli)\ **Replies:** 15\ **Last updated:** [March 16, 2024, 10:04pm UTC](https://racket.discourse.group/t/read-access-denied-for/1834 "2024-03-16T22:04:42Z")
Hi! Newish to Racket and I hope this is appropriate. I am going thought the material in Berkeley's CS61A and I am running into the following error when I run their autograder locally as in racket -tm grader.rkt -- hw1-… --- ## [Examples of 2htdp/universe programs with a server](https://racket.discourse.group/t/examples-of-2htdp-universe-programs-with-a-server/2794)
**Author:** [@maueroats](https://racket.discourse.group/u/maueroats)\ **Replies:** 1\ **Last updated:** [March 16, 2024, 1:16pm UTC](https://racket.discourse.group/t/examples-of-2htdp-universe-programs-with-a-server/2794 "2024-03-16T13:16:31Z")
The Universe teachpack comes with a server and a way for big-bang clients to communicate with the server. I know that Marco Morazan's book includes material teaching how to use this system. I am also aware that the off… --- ## [Is there a way to outline certain pen strokes used when drawing a \`pict\`?](https://racket.discourse.group/t/is-there-a-way-to-outline-certain-pen-strokes-used-when-drawing-a-pict/2761)
**Author:** [@benknoble](https://racket.discourse.group/u/benknoble)\ **Replies:** 4\ **Last updated:** [March 15, 2024, 2:38pm UTC](https://racket.discourse.group/t/is-there-a-way-to-outline-certain-pen-strokes-used-when-drawing-a-pict/2761 "2024-03-15T14:38:37Z")
I have some picts that I'm hoping to make useful on both light and dark backgrounds. One way I envisioned to do so was to outline black pen strokes with white strokes, so that on either kind of background one of the stro… --- ## [Enumerated stream](https://racket.discourse.group/t/enumerated-stream/2790)
**Author:** [@Tyrn](https://racket.discourse.group/u/Tyrn)\ **Replies:** 4\ **Last updated:** [March 14, 2024, 11:38pm UTC](https://racket.discourse.group/t/enumerated-stream/2790 "2024-03-14T23:38:31Z")
Hi, Suppose I have something like this: (define reds (stream-cons "red" reds)) (stream-for-each displayln reds)) The output will be red red red ... What's the Racket way to make it 1 red 2 red 3 red ... ? --- ## [Scheme+ v7.5 for Racket](https://racket.discourse.group/t/scheme-v7-5-for-racket/2784)
**Author:** [@damien\_mattei](https://racket.discourse.group/u/damien_mattei)\ **Replies:** 0\ **Last updated:** [March 12, 2024, 10:51pm UTC](https://racket.discourse.group/t/scheme-v7-5-for-racket/2784 "2024-03-12T22:51:56Z")
Hello, i released the version 7.5 of Scheme+ for Racket. https://github.com/damien-mattei/Scheme-PLUS-for-Racket it is also available has a Racket package here: https://pkgd.racket-lang.org/pkgn/package/Scheme-PLUS-f… --- ## [Issues running a net/rfc6455 web-socket server on Windows](https://racket.discourse.group/t/issues-running-a-net-rfc6455-web-socket-server-on-windows/2729)
**Author:** [@tnelson](https://racket.discourse.group/u/tnelson)\ **Replies:** 5\ **Last updated:** [March 12, 2024, 5:54pm UTC](https://racket.discourse.group/t/issues-running-a-net-rfc6455-web-socket-server-on-windows/2729 "2024-03-12T17:54:05Z")
Hi, I'm having trouble getting a web-socket server (via Racket's net/rfc6455 package) to work properly in Windows. Concretely, if I run the server in DrRacket or via WSL or git bash, everything works fine. However, if I… --- ## [\`raco exe ++lang\`?](https://racket.discourse.group/t/raco-exe-lang/2780)
**Author:** [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Replies:** 0\ **Last updated:** [March 12, 2024, 2:31am UTC](https://racket.discourse.group/t/raco-exe-lang/2780 "2024-03-12T02:31:58Z")
Suppose I have a program which dynamic-requires source files using a #lang language whose reader does not implement a get-info function that supports the 'module-language key. For instance, #lang racket (require racket… [Previous page](https://racket.discourse.group/latest.md?page=30) [Next page](https://racket.discourse.group/latest.md?page=32)