[racket-users] Animation-problem

[Janiho]

Hello!

The animation in this Pet Shop boys music video (LINK: 
https://www.youtube.com/watch?v=lNLkcOqQSBM (very good song btw!))

gave me a inspiration try to make it with the Racket.

I'm very novice using the Racket, so I got to dead-end early.
 

I get this far:

(require 2htdp/universe)
(require 2htdp/image)


(define SUPER (overlay (text "SUPER" 105 (make-color (random 255)
(random 255)
(random 255)))

   (circle 200 "solid" (make-color (random 255)
(random 255)
(random 255)


SUPER

--

This code does one figure. Now the problem is how I can make them in a row and 
changing colors at the same time. I just don't understand how to get different 
figures in racket's memory. 

Any advices, what might be the easiest way to do it? Using 
map/foldl/place-image -commands maybe? 
 

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Re: [racket-users] Animation-problem

[Daniel Prager]

Hi Janiho

This should help get you get going ...

The function big-bang takes minimally:
*  an initial "state of the world",
* a function that  that takes the current world state and evolves it with
every tick of a notional clock, and
* a function that takes the state of the world and draws it.

In this case there's no dependence on the existing state, so the function
random-state ignores what is passed in, but it has the necessary form to
work with big-bang.

Exercise: add a counter to the world state that increments with every tick,
and show this as a number in the top-left corner of the animated image.

Dan


#lang racket

(require 2htdp/universe)
(require 2htdp/image)

(struct world (foreground background))

(define (random-color)
  (make-color (random 255) (random 255) (random 255)))

(define (random-state current)
  (world (random-color) (random-color)))

(define (SUPER state)
  (overlay (text "SUPER" 105 (world-foreground state))
   (circle 200 "solid" (world-background state

(big-bang (random-state null)
  (on-tick random-state 0.3) ; change the image every 0.3 seconds
  (to-draw SUPER))

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Re: [racket-users] Re: Language-provided bindings and arrows in DrRacket

[Dupéron Georges]

Le dimanche 4 décembre 2016 04:18:44 UTC+1, Robby Findler a écrit :
> The fully expanded form of the original program doesn't have a require
> that brings in displayln?

Indeed, if I use (#%require lng) the arrows get drawn.

However, the body can require libraries which shadow some of the 
language-provided bindings, e.g. (require type-expander) shadows some of the 
bindings imported by #lang typed/racket. I therefore use (#%require (only lng)) 
to make sure the lng module is available, without creating potential conflicts 
with other required modules.

I was hoping there would be some trick similar to disappeared-use and 
disappeared-bindings that would help me solve this problem. I suppose I could 
apply a 'disappeared-binding property to the "racket/base" on the second line, 
using a list containing every binding imported by the "module language".

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Re: [racket-users] Re: Language-provided bindings and arrows in DrRacket

[Dupéron Georges]

I think I found a solution which allows me to inject the (#%require lng) 
without causing conflicts with other required module: applying an extra scope 
to the whole body makes the other (require) forms more specific, and they can 
shadow bindings imported by (#%require lng).

Here is the modified "MyLang.rkt":

#lang racket
(provide (rename-out [my-module-begin #%module-begin]))
(define-syntax (my-module-begin stx)
  (syntax-case stx ()
[(_ real-lang body)
 (syntax-case (local-expand #'(module m real-lang body) 'top-level (list)) 
()
   [(module nm lng (#%plain-module-begin . body2))
#`(#%plain-module-begin
 (#%require lng)
 . #,((make-syntax-introducer) #'body2))])]))

And here's an example file using it:

(module m "MyLang.rkt"
  ;; delegates to this language:
  typed/racket/base
  ;; body:
  (begin
(require racket/set)
(displayln ;; arrow successfully drawn to typed/racket/base
 (set  ;; arrow successfully drawn to racket/set
  "Hello"

Without the extra scope, I would get this error because racket/set shadows 
these bindings imported by typed/racket/base:

module: identifier already imported from a different source in:
  for/set
  racket/set
  typed/racket/base

My problem seems solved, but if this extra-scope trick has some unwanted 
consequences, I would definitely want to hear about them!

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Re: [racket-users] Language-provided bindings and arrows in DrRacket

[Alex Knauth]

> On Dec 4, 2016, at 10:27 AM, Dupéron Georges  
> wrote:
> 
> I think I found a solution which allows me to inject the (#%require lng) 
> without causing conflicts with other required module: applying an extra scope 
> to the whole body makes the other (require) forms more specific, and they can 
> shadow bindings imported by (#%require lng).

A nested scope seems like the correct solution. The macro expander does 
something similar with module body's, but it creates a pair of scopes for the 
body. I'm not sure whether you would need to do the same...

http://www.cs.utah.edu/plt/scope-sets/general-macros.html#%28part._.Modules_and_.Phases%29
 


I can't see any unwanted consequences of this approach, but I also don't know 
much about how scopes work with requires.

Alex Knauth

> Here is the modified "MyLang.rkt":
> 
> #lang racket
> (provide (rename-out [my-module-begin #%module-begin]))
> (define-syntax (my-module-begin stx)
>  (syntax-case stx ()
>[(_ real-lang body)
> (syntax-case (local-expand #'(module m real-lang body) 'top-level (list)) 
> ()
>   [(module nm lng (#%plain-module-begin . body2))
>#`(#%plain-module-begin
> (#%require lng)
> . #,((make-syntax-introducer) #'body2))])]))

> My problem seems solved, but if this extra-scope trick has some unwanted 
> consequences, I would definitely want to hear about them!


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Re: [racket-users] Reducing Program Startup Time

[Matthias Felleisen]

> On Dec 3, 2016, at 9:40 PM, Dupéron Georges  
> wrote:
> 
> A few ideas:
> 
> 1) Loading a lot of modules can be slow. You are already avoiding that by 
> using racket/base and racket/gui/base, so that's good, but it already takes 
> me 0.5s just to require these :-( . I don't know it there is much to do about 
> this.


Also consider lazy require. 

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Re: [racket-users] Reducing Program Startup Time

[Lehi Toskin]

Dupéron Georges I did what you suggested and placed a displayln at the 
beginning. There's a wait time between when I execute the program and then 
everything happens all at once - the displayln occurs at the same time as when 
the GUI spawns.

> On Sunday, December 4, 2016 at 10:05:23 AM UTC-8, Matthias Felleisen wrote:
> 
> Also consider lazy require.

That actually seems to make it run slower.

$ time ./ivy -V
Ivy 1.2

real0m2.414s
user0m2.288s
sys 0m0.119s

versus

$ time /usr/bin/ivy -V
Ivy 1.2

real0m1.955s
user0m1.796s
sys 0m0.147s

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