[racket] Defining a typed language

Konrad Hinsen writes: > Then, a module that uses it: > >#lang s-exp "my-typed-lang.rkt" > >(define-foo x) After a closer look at the language definition mechanism, I came to the conclusion that the language here is actually "s-exp", with my module merely providing the initial bindi

Re: [racket] Understanding contracts

Where are you calling `cubic-bezier` from? If its from the REPL, the module itself, or a submodule the function won’t have a contract attached. Only code outside `cubic-bezier`s module will have the version of `cubic-bezier` with a contract attached. On Wed, Oct 1, 2014 at 9:46 PM, Alexander Mc

Re: [racket] A beginner's question re drawing on a canvas

Chris, It sounds like your mental model of the canvas is that stuff you draw on it stays there permanently, like paint on a real-world canvas. This is not how the GUI works. When the GUI canvas is displayed on the screen, it asks your program (by calling on-paint) to draw the canvas contents

Re: [racket] A beginner's question re drawing on a canvas

Thanks everyone - amazingly helpful and quick reponses! crystal clear code - thanks Sean The MVC analogy is very helpful. I think I have some old Apple SmallTalk discs lying around! Cheers Chris On 2 October 2014 12:44, Justin Zamora wrote: > You should learn about Model-View-Controller arch

[racket] Understanding contracts

Hello, I've been working on a sample project to better understand how to use the contract system. I created a simple Bezier curve implementation and am using (provide (contract-out...) to attach contracts to the provided bindings. Basically I have a procedure called cubic-bezier that accepts two

Re: [racket] A beginner's question re drawing on a canvas

You should learn about Model-View-Controller architecture (for example at http://en.m.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller). Briefly, the model is a data structure that represents the information you are working with. The view is able to produce a visual representation of the m

Re: [racket] A beginner's question re drawing on a canvas

At the risk of sending duplicate information, and you should prefer Matthias' responses as he is far more experienced, but one idea is to place all drawing code under the canvas class definition. Then the button callback should invoke that class' new drawing method. This keeps the actual drawing co

Re: [racket] A beginner's question re drawing on a canvas

Thanks Matthias and Sean It's often helpful when people asking questions ask them clearly ! :) I'll now attempt a clarification... say I have a button in the window, and when that button is pressed, I want to draw on the canvas - and later, another button is pressed, and I might want to draw some

Re: [racket] A beginner's question re drawing on a canvas

Hi, Just make the drawing code part of on-paint. I have inlined a subclass for you: #lang racket/gui (define frame (new frame% [label "Example"] [width 300] [height 300])) (define top-canvas (new (class canvas% (super-new [parent frame])

Re: [racket] A beginner's question re drawing on a canvas

Does this help? #lang racket/gui (define frame (new frame% [label "Example"] [width 300] [height 300])) (define top-canvas (new (class canvas% (inherit get-dc) (super-new [parent frame]) (define/override (on-paint) (define dc (get-

[racket] A beginner's question re drawing on a canvas

I would like to draw on a canvas in a window at various times during program execution. My first attempt was to combine two examples: #lang racket/gui (define frame (new frame% [label "Example"] [width 300] [height 300])) (define top-canvas

Re: [racket] strange behaviour of a (match) form

Oh! Really. Thank you! Sorry, I am not experienced in Racket. 2014-10-02 0:56 GMT+04:00 Matthias Felleisen : > > In this context, null is just a variable and it gets bound to what it > matches: > > > Welcome to Racket v6.1.0.8. > > > (match 'hello-world [null null]) > > 'hello-world > > > > On O

Re: [racket] strange behaviour of a (match) form

In this context, null is just a variable and it gets bound to what it matches: > Welcome to Racket v6.1.0.8. > > (match 'hello-world [null null]) > 'hello-world On Oct 1, 2014, at 4:52 PM, Yuri Garmay wrote: > Hi, all > > Accidentally, I found out that null matchs in unexpected way (seems

[racket] strange behaviour of a (match) form

Hi, all Accidentally, I found out that null matchs in unexpected way (seems it matchs always) So, (define (length-my list) (match list ['() 0] [(cons x xs) (+ 1 (length-my xs))] [_ 'not-a-list])) (length-my '(1 2 3 4)) >produces 4 But (define (length-my list) (match

[racket] Another (scientific) website powered by Racket

Hello, Just in case anybody is keeping track of Racket use cases worldwide: here is a web site written entirely in Racket http://ephemeris.ipa.nw.ru/ The site is rather simple. It produces astronomical ephemeris tables for the chosen body of the Solar System for specified dates. Racket is cred

[racket] Defining a typed language

Hi everyone, I'd like to define my own language that produces modules and code considered "typed", as in Typed Racket. In fact, my language is just a subset of Typed Racket plus a few new macros. I started by writing "my-typed-lang.rkt": #lang typed/racket (provide define-foo