Re: [racket-users] What do you use macros for?
Late to the party, and to make life simple, I removed all quoted material. Asumu quoted me from the early 1990s. That's what I understood back then about macros and I got on the wrong track with this idea for about five to eight years. I wanted macros to become complete language definitions ... and that's what they are good for, but there is way more in all directions. So here are two thoughts. First credit to Kent Dybvig who bluntly said to me in '97 or so, I want to be able to define macros inside of some lexical scope. These days I define little macros inside of loops or methods all the time. Here is an example: (define/public (run) (parameterize ([current-input-port in] [current-output-port out]) (send-message SIGN-UP) (define ok (read-json in)) (define/fsm start (state: start json->start void --> choose) (state: choose json->choose (compose send-message values) --> feed-next) (state: feed-next json->state next->json --> feed-next || start The above is a remote proxy that will receive three kinds of messages on port 'in' and will respond via a call to a proper class. Then it transitions to a different state where it will wait for a different kind of input. The define/fsm macro makes this incredible easy to express. I bet everyone can read this 3-line FSM and guess what each transition does: -- in state 'feed-next', the method reads the message with json->state -- calls the method feed-next of the contained object -- sends the result off to the 'out' port with next->json -- and then transitions to either feed-next or start, depending on what kind of message arrives. The 10-line macro refers to pieces of the class and cannot be defined globally. Second credit to Matthew (and Shriram and Robby) who kept me on the 'macros are good for designing complete languages' track, too. This one is important for different reasons. Often you want to create a reasonably complete language but not invent everything from scratch. In our words, you want 'linguistic inheritance'. For example, you like Haskell's type system but you hate, loathe, despise the stupid idea of universally lazy evaluation. Well, if you were in Racket, you'd define a 10-line language that looks, feels, smells, tastes like the host but has a by-value evaluation mechanism. Of course, Racket is by-value, so you may convert it into a lazy language without giving up the lovely parentheses and the beautiful Lisp syntax. Well, it's a 10-line language definition, based on Racket's generalization of old, very old, stone-age old Lisp macro system. See the last chapter of Realm of Racket on how to teach Kindergarden kids to define this kind of by-need (actually by-name) Racket. In short, as Robby says 'macros' (what a stupid word) serve the whole range of purposes, from little conveniences inside of a class to entire language rewrites that keep the best of one language and add better things on top -- Matthias -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Racket change button% coordinates(X and Y axis)
At Sun, 10 Apr 2016 08:18:50 -0700 (PDT), Theodor Berza wrote: > The purpose of this project is to make a GUI Builder where the user drags > buttons on a frame and the position of the cursor changes in the code the X > and Y axis. I case you haven't found it already, you might want to take a look at this GUI builder: https://github.com/Metaxal/MrEd-Designer To answer your question more directly, you could create a panel with a custom layout function to directly position children: http://docs.racket-lang.org/gui/windowing-overview.html#%28part._new-containers%29 I think MrEd Designer uses the pasteboard approach that Jens Axel suggests, though. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] Hidden a list
Hello guys,
There any way to hide the contents of a list as does the structure?
(define lst (list "abc" 123 (+ 12 32)))
lst ; --> '("abc" 123 44) something like #
(define-struct user (nom ape))
(define u (make-user "nom" "ape"))
user ; --> #
u ; --> #
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Re: [racket-users] Hidden a list
You could write your own printer, that recognizes lists specially and
prints them how you want, and set the `current-print` parameter.
Or you could use an opaque struct type and wrap your lists with those
structs.
Vincent
On Mon, 11 Apr 2016 10:35:55 -0500,
Héctor Mc wrote:
>
> Hello guys,
>
> There any way to hide the contents of a list as does the structure?
>
> (define lst (list "abc" 123 (+ 12 32)))
> lst ; --> '("abc" 123 44) something like #
>
> (define-struct user (nom ape))
> (define u (make-user "nom" "ape"))
> user ; --> #
> u ; --> #
>
> --
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
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[racket-users] Racket's UDP Behavior
I'm building reliable data transfer onto Racket's UDP suite for a term project, and I need to know what Racket does with corrupt datagrams. Since the Racket docs don't mention the word checksum for the UDP segment, I need to know some things: * Does Racket just throw away corrupt datagrams? ** Does it then notify the program that's running (udp-receive!)? * When it detects a corrupt datagram, does it do something as radical as contact the sender for retransmission? I can't build reliable data transfer until I can be sure I'm not losing datagrams in the ether, and I don't know how to accomplish this. Is there a preferred workaround for this (as in continued retransmission until the datagram successfully reaches its destination)? Thanks, Nick -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Racket's UDP Behavior
On 04/11/2016 01:52 PM, Nick Gordon wrote: > I'm building reliable data transfer onto Racket's UDP suite for a > term project, and I need to know what Racket does with corrupt > datagrams. Since the Racket docs don't mention the word checksum for > the UDP segment, I need to know some things: The kernel discards corrupt UDP datagrams, so Racket doesn't see them. There is certainly *no* automatic retransmission involved. > I can't build reliable data transfer until I can be sure I'm not > losing datagrams in the ether, and I don't know how to accomplish > this. Is there a preferred workaround for this (as in continued > retransmission until the datagram successfully reaches its > destination)? Yes, effectively this. I recommend reading up on protocols for achieving "reliable" delivery on unreliable networks. For example, look into how TCP works. (Bear in mind that UDP is basically the same thing as IP.) One of your first tasks will be to decide what "reliable" means in your context. If you haven't seen it before, check out the Fischer-Lynch-Patterson Impossibility Result: http://the-paper-trail.org/blog/a-brief-tour-of-flp-impossibility/ Also, look into the Byzantine Generals problem: https://en.wikipedia.org/wiki/Byzantine_fault_tolerance Once you understand why the Byzantine Generals problem has no solution, you can start to work toward making a decision about how your "reliable" system should behave in corner cases. Tony -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Re: Problem with # and mutable lists
> > but although I changed else expresion, Racket sometimes returns same > warning(but now with #f instead of #). After you call `select-room`, you'll want to check that the result is an mlist (instead of #f or #) before calling mcdr. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] Re: What do you use macros for?
On Mon, 11 Apr 2016 10:25:46 -0400, Matthias Felleisen wrote: >These days I define little macros inside of loops or methods all the time. Same here. My most common uses are to handle database connections and to embed free form SQL into Racket code. George -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Re: What do you use macros for?
On Apr 12, 2016 7:53 AM, "George Neuner" wrote: > > On Mon, 11 Apr 2016 10:25:46 -0400, Matthias Felleisen > wrote: > > >These days I define little macros inside of loops or methods all the time. > > Same here. My most common uses are to handle database connections and > to embed free form SQL into Racket code. > > George > Care to post one of your examples, with a bit of commentary? Dan -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] Questions about implementing a Lisp-2
Hello Racketeers, I come seeking advice. I'm trying to implement a Lisp-2 in Racket, but I've been unsuccessful in my initial attempts. My goal is to be able to do something like the following: ``` (defun example (sym) (symbol->string sym)) (defvar example 'an-arbitrary-symbol) (example example) ;=> "an-arbitrary-symbol" ``` And my here was my first stab at a solution: ``` #lang racket (define-for-syntax functions-ns (make-empty-namespace)) (define-for-syntax values-ns (make-empty-namespace)) (define-syntax (defun stx) (syntax-case stx () [(_ name (arg ...) body0 body ...) (parameterize ([current-namespace functions-ns]) #'(define (name arg ...) body0 body ...))])) (define-syntax (defvar stx) (syntax-case stx () [(_ name value) (parameterize ([current-namespace values-ns]) #'(define name value))])) ;; Let's see whether these work. (defvar example 'an-arbitrary-symbol) (defun example (sym) (symbol->string sym)) (example example) ;;=> symbol->string: contract violation ;;=> expected: symbol? ;;=> given: # ;;=> context...: ;;=>/opt/homebrew-cask/Caskroom/racket/6.4/Racket v6.4/collects/racket/private/misc.rkt:87:7 ``` I'll be deeply grateful for help you can provide. Cheers, Josh -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Questions about implementing a Lisp-2
Josh Tilles wrote on 04/11/2016 07:51 PM: I'm trying to implement a Lisp-2 in Racket, I would first decide whether and how I want functions and variables provided by modules in this language, to be usable from modules in other `#lang`s. That narrows down the options of how to do it. If you're writing an Emacs Lisp implementation, I would look at what Guile has done. And also consider whether the dynamically-scoped and buffer-local variables affect how you solve your Lisp-2 namespaces problem. Neil V. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Questions about implementing a Lisp-2
Messing with `current-namespace` seems like overkill, though maybe this approach is too naive for your needs, which just involves hiding the `defun` identifiers in the current namespace with a `defun:` prefix, then using `#%app` to pull them out again. #lang racket (require rackunit (for-syntax racket/syntax) (prefix-in rb: (only-in racket/base #%app))) (define-syntax (defun stx) (syntax-case stx () [(_ name (arg ...) body0 body ...) (with-syntax ([defun:name (format-id stx "defun:~a" #'name)]) #'(define (defun:name arg ...) body0 body ...))])) (define-syntax-rule (defvar name value) (define name value)) (define-syntax (#%app stx) (syntax-case stx () [(_ proc-name args ...) (with-syntax ([defun:proc-name (format-id stx "defun:~a" #'proc-name)]) (if (identifier-binding #'defun:proc-name) #'(rb:#%app defun:proc-name args ...) #'(rb:#%app proc-name args ...)))])) ;; Let's see whether these work. (defvar example 'an-arbitrary-symbol) (defun example (sym) (symbol->string sym)) (check-equal? (example example) "an-arbitrary-symbol") (check-equal? (symbol->string example) "an-arbitrary-symbol") On Apr 11, 2016, at 4:51 PM, Josh Tilles wrote: > Hello Racketeers, > > I come seeking advice. I'm trying to implement a Lisp-2 in Racket, but I've > been unsuccessful in my initial attempts. > > My goal is to be able to do something like the following: > > ``` > (defun example (sym) > (symbol->string sym)) > > (defvar example 'an-arbitrary-symbol) > > (example example) > ;=> "an-arbitrary-symbol" > ``` > > And my here was my first stab at a solution: > > ``` > #lang racket > > (define-for-syntax functions-ns (make-empty-namespace)) > (define-for-syntax values-ns (make-empty-namespace)) > > (define-syntax (defun stx) > (syntax-case stx () >[(_ name (arg ...) body0 body ...) > (parameterize ([current-namespace functions-ns]) > #'(define (name arg ...) > body0 > body ...))])) > > (define-syntax (defvar stx) > (syntax-case stx () >[(_ name value) > (parameterize ([current-namespace values-ns]) > #'(define name value))])) > > ;; Let's see whether these work. > (defvar example 'an-arbitrary-symbol) > (defun example (sym) (symbol->string sym)) > (example example) > ;;=> symbol->string: contract violation > ;;=> expected: symbol? > ;;=> given: # > ;;=> context...: > ;;=>/opt/homebrew-cask/Caskroom/racket/6.4/Racket > v6.4/collects/racket/private/misc.rkt:87:7 > ``` > > I'll be deeply grateful for help you can provide. > > Cheers, > Josh > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Re: What do you use macros for?
Today I decided to convert all structure definitions in a Typed Racket file to lists. For instance, (struct foo ([x : Integer])) would become a tagged list: (define-type foo (Pairof 'foo (List Integer))) along with a constructor, predicate, and accessors. Using a macro, I was able to write what I wanted to do once and use it for multiple structures. Here's how it looked in one file: all I had to do was write the macro, use "struct2" instead of "struct", and remove uses of "struct-out". Other files in the project worked with the new data definition, no problems. #lang typed/racket (require (for-syntax racket/base syntax/parse racket/syntax)) (define-syntax (struct2 stx) (syntax-parse stx #:datum-literals (:) [(_ name:id ([f*:id : t*] ...)) #:with ((name-f* i*) ...) (for/list ([f (in-list (syntax-e #'(f* ...)))] [i (in-naturals 1)]) (list (format-id stx "~a-~a" (syntax-e #'name) (syntax-e f)) i)) #:with Name (format-id stx "~a" (string-titlecase (symbol->string (syntax-e #'name #:with name? (format-id stx "~a?" (syntax-e #'name)) (syntax/loc stx (begin (define-type Name (Pairof 'name (Listof Any))) (provide Name) (define (name (f* : t*) ...) : Name (list 'name f* ...)) (provide name) (define (name-f* (p : Name)) : t* (cast (list-ref p 'i*) t*)) ... (provide name-f* ...) (define (name? (v : Any)) : Boolean (and (list? v) (not (null? v)) (eq? 'name (car v ))])) (struct2 posn ([x : Real] [y : Real])) (struct2 block ([x : Real] [y : Real] [color : Symbol])) (struct2 tetra ([center : Posn] [blocks : (Listof Block)])) (struct2 world ([tetra : Tetra] [blocks : (Listof Block)])) (: posn=? (-> Posn Posn Boolean)) (define (posn=? p1 p2) (and (= (posn-x p1) (posn-x p2)) (= (posn-y p1) (posn-y p2 (provide posn=?) (Nevermind why I did this, or why I used "Any" and "cast". Hopefully the macro is interesting.) -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] DrRacket 6.4 error message + a misleading message
Hi All, we have discovered that in 6.4 DrRacket (Advanced Student) seems to have a bug generating error messages for foldl/foldr: (foldl + (list 2 3 4) 0) gives an error message "foldl: 2th argument must be a list, given 0" (in addition to the incorrect "th" for "2nd", the 0 is actually the third argument, not second). There is also a somewhat misleading error (for beginners) in 6.4 and earlier versions, shown with a somewhat artificial example: (map (lambda (x y) (+ x y)) (list 2 3 4)) gives and error: the given procedure's expected number of arguments does not match the given number of lists given procedure: # expected: 2 given: 1 This is technically correct, but not understandable to a student since most likely they mistakenly used a two-argument function instead of a one-argument one. In fact, students are never shown a map with multiple lists. A better message would say that a one-argument function was expected, but a two-argument function was given. The second error is somewhat of a design choice, but the first one (with foldl) is a bug. If there is a way to patch it in 6.4, that would be greatly appreciated. Cheers, Elena -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] DrRacket 6.4 error message + a misleading message
Thanks for the bug report. I can confirm the error, and I will check into it tomorrow morning. > On Apr 11, 2016, at 9:25 PM, Elena Machkasova wrote: > > Hi All, > > we have discovered that in 6.4 DrRacket (Advanced Student) seems to have a > bug generating error messages for foldl/foldr: > > (foldl + (list 2 3 4) 0) > > gives an error message "foldl: 2th argument must be a list, given 0" > (in addition to the incorrect "th" for "2nd", the 0 is actually the third > argument, not second). > > There is also a somewhat misleading error (for beginners) in 6.4 and earlier > versions, shown with a somewhat artificial example: > > (map (lambda (x y) (+ x y)) (list 2 3 4)) > > gives and error: > > the given procedure's expected number of arguments does not match > the given number of lists > given procedure: # > expected: 2 > given: 1 > > This is technically correct, but not understandable to a student since most > likely they mistakenly used a two-argument function instead of a one-argument > one. In fact, students are never shown a map with multiple lists. A better > message would say that a one-argument function was expected, but a > two-argument function was given. > > The second error is somewhat of a design choice, but the first one (with > foldl) is a bug. If there is a way to patch it in 6.4, that would be greatly > appreciated. > > Cheers, > Elena > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
