532 lines
22 KiB
Racket
532 lines
22 KiB
Racket
#lang meta/web
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(require "resources.rkt" "code.rkt" "download.rkt" "learning.rkt")
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(define (doc path . text)
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(apply a href: (list "http://docs.racket-lang.org/" path) text))
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(struct example (code desc))
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(define ((example-with-help . help) code desc) (example code (list desc help)))
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(define generic-example
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@example-with-help{
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@p{To run the example, install Racket, start DrRacket, paste the example
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program into the top area in DrRacket, and click the Run button.
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Alternatively, save the program to a file and run @tt{racket} on the
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file.}})
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(define cmdline-example
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@example-with-help{
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@p{This example is a command-line script. To run the example, install
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Racket, paste the example program into a file, and run @tt{racket} on
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the file with command-line arguments after the filename. Alternatively,
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for a Unix installation, you can add @tt{#!/usr/bin/env racket} at the
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top and make the file executable, and then you can run the file
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directly.}})
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(define scribble-example
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@example-with-help{
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@p{To run the example, install Racket, start DrRacket, and paste the
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example program into the top area in DrRacket. When a program in a
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Scribble language is opened in DrRacket, a @b{Scribble HTML} button
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appears for rendering the document to HTML. Click it.}})
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(define graphical-example
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@example-with-help{
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@p{To run the example, install Racket, start DrRacket, paste the example
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program into the top area in DrRacket, and click the Run button.}})
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(define desc div)
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(define (elemcode . strs) (apply tt strs))
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(define examples
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@; --- Each example here should at most 7 lines long ---------------
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(list
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@; Candidates for initial example: --------------------------------
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(list
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(generic-example ; -----------------------------------------------
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@code{#lang racket
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;; Finds Racket sources in all subdirs
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(for ([path (in-directory)])
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(when (regexp-match? #rx"[.]rkt$" path)
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(printf "source file: ~a\n" path)))}
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@desc{The @elemcode{in-directory} function constructs a sequence that
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walks a directory tree (starting with the current directory, by default)
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and generates paths in the tree. The @elemcode{for} form binds
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@elemcode{p} to each path in the sequence, and @elemcode{regexp-match?}
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applies a pattern to the path.})
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(generic-example ; -----------------------------------------------
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@code{#lang web-server/insta
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;; A "hello world" web server
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(define (start request)
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(response/xexpr
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'(html
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(body "Hello World"))))}
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@desc{This example implements a web server using the
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@elemcode{web-server/insta} language. Each time a connection is made to
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the server, the @elemcode{start} function is called to get the HTML to
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send back to the client.})
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(generic-example ; -----------------------------------------------
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@code{#lang racket ; An echo server
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(define listener (tcp-listen 12345))
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(let echo-server ()
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(define-values (in out) (tcp-accept listener))
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(thread (lambda () (copy-port in out)
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(close-output-port out)))
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(echo-server))}
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@desc{Racket makes it easy to use TCP sockets and spawn threads to handle
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them. This program starts a server at TCP port 12345 that echos
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anything a client sends back to the client.})
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(generic-example ; -----------------------------------------------
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@code{#lang racket
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;; Report each unique line from stdin
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(let ([saw (make-hash)])
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(for ([line (in-lines)])
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(unless (hash-ref saw line #f)
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(displayln line))
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(hash-set! saw line #t)))}
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@desc{Uses a hash table to record previously seen lines. You can run this
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program in DrRacket, but it makes more sense from the command line.}))
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@; Additional examples: -------------------------------------------
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(list
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(graphical-example ; ---------------------------------------------
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@code{#lang racket ; A picture
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(require 2htdp/image)
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(let sierpinski ([n 8])
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(if (zero? n)
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(triangle 2 'solid 'red)
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(let ([t (sierpinski (- n 1))])
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(freeze (above t (beside t t))))))}
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@desc{The @elemcode{2htdp/image} library provides easy-to-use functions
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for constructing images, and DrRacket can display an image result as
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easily as it can display a number result. In this case, a
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@elemcode{sierpinski} function is defined and called (at the same time)
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to generate a Sierpinski triangle of depth 8.})
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(graphical-example ; ---------------------------------------------
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@code{#lang racket/gui ; A GUI guessing game
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(define f (new frame% [label "Guess"]))
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(define n (random 5)) (send f show #t)
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(define ((check i) btn evt)
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(message-box "." (if (= i n) "Yes" "No")))
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(for ([i (in-range 5)])
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(make-object button% (format "~a" i) f (check i)))}
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@desc{This simple guesing game demonstates Racket's class-based GUI
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toolkit. The @elemcode{frame%} class implements a top-level window, and
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@elemcode{button%} obviously implements a button. The @elemcode{check}
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function defined here produces an function that is used for the button's
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callback action.})
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(generic-example ; -----------------------------------------------
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@code{#lang racket ; Simple web scraper
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(require net/url net/uri-codec)
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(define (let-me-google-that-for-you str)
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(let* ([g "http://www.google.com/search?q="]
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[u (string-append g (uri-encode str))]
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[rx #rx"(?<=<h3 class=\"r\">).*?(?=</h3>)"])
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(regexp-match* rx (get-pure-port (string->url u)))))}
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@desc{Add a call to @elemcode{let-me-google-that-for-you} to get a list of
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search results.})
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(cmdline-example ; -----------------------------------------------
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@code{#lang racket
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;; A dice-rolling command-line utility
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(command-line
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#:args (dice sides)
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(for ([i (in-range (string->number dice))])
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(displayln
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(+ 1 (random (string->number sides))))))}
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@desc{Playing a game but no dice on hand? Let Racket roll for you. The
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@elemcode{command-line} form makes sure that the right number of
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arguments are provided and automatically implements the @tt{--help}
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switch.})
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(generic-example ; -----------------------------------------------
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@code{#lang racket
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;; Print the Greek alphabet
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(for ([i (in-range 25)])
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(displayln
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(integer->char
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(+ i (char->integer #\u3B1)))))}
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@desc{The only reason we use the encoded form of a character
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@elemcode{#\u3B1} instead of the more direct form @elemcode{#\α} is that
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we don't trust your browser to render it correctly. DrRacket is
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perfectly happy with @elemcode{#\α}.})
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(graphical-example ; ---------------------------------------------
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@code{#lang htdp/bsl ; Any key inflates the balloon
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(require 2htdp/image) (require 2htdp/universe)
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(define (balloon b) (circle b "solid" "red"))
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(define (blow-up b k) (+ b 5))
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(define (deflate b) (max (- b 1) 1))
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(big-bang 50 (on-key blow-up) (on-tick deflate)
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(to-draw balloon 200 200))}
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@desc{Racket's mission includes education at all levels. This program
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uses the @elemcode{htdp/bsl} teaching language, the
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@elemcode{2htdp/image} library for creating pictures in the teaching
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languages, and the @elemcode{2htdp/universe} library for interactive
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animations.})
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(generic-example ; -----------------------------------------------
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@code{#lang lazy
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;; An infinite list:
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(define fibs
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(list* 1 1 (map + fibs (cdr fibs))))
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@||
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;; Print the 1000th Fibonacci number:
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(print (list-ref fibs 1000))}
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@desc{And now for something completely different. The @elemcode{lazy}
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language is more like Haskell than Lisp, so feel free to build an
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infinite list and look at only part of it.})
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(generic-example ; -----------------------------------------------
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@code{#lang typed/racket
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;; Using higher-order occurrence typing
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(define-type SrN (U String Number))
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(: tog ((Listof SrN) -> String))
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(define (tog l)
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(apply string-append (filter string? l)))
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(tog (list 5 "hello " 1/2 "world" (sqrt -1)))}
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@desc{Racket's type system is designed to let you add types after you've
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worked for a while in untyped mode — even if your untyped program
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wouldn't fit nicely in a conventional type system.})
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(scribble-example ; ----------------------------------------------
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@code|{#lang scribble/base
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@; Generate a PDF or HTML document
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@title{Bottles --- @italic{Abridged}}
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@(apply itemlist
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(for/list ([n (in-range 100 0 -1)])
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@item{@(format "~a" n) bottles.}))}|
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@desc{This program uses the @elemcode{scribble/base} language for
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generating documents using a prose-friendly syntax.})
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(graphical-example ; ---------------------------------------------
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@code{#lang racket ; draw a graph of cos
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(require plot) ; and deriv^3(cos)
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(define ((deriv f) x)
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(/ (- (f x) (f (- x 0.001))) 0.001))
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(define (thrice f) (lambda (x) (f (f (f x)))))
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(plot (list (function ((thrice deriv) sin) -5 5)
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(function cos -5 5 #:color 'blue)))}
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@desc{This program uses the @elemcode{plot} library to draw plots of
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functions. Note that the plots are actual value, which DrRacket shows
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in graphical form.})
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(generic-example ; -----------------------------------------------
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@code{#lang racket ; Sending email from racket
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(require net/sendmail)
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(sleep (* (- (* 60 4) 15) 60)) ; 4h - 15m
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(send-mail-message
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(getenv "EMAIL") "Parking meter alert!"
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(list (getenv "EMAIL")) null null
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'("Time to go out and move your car."))}
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@desc{Racket comes with plenty of libraries.})
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(generic-example ; -----------------------------------------------
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@code{#lang scheme/base ; Simple use of the FFI
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(require ffi/unsafe)
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(define mci-send-string
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(get-ffi-obj "mciSendStringA" "Winmm"
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(_fun _string [_pointer = #f] [_int = 0]
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[_pointer = #f] -> [ret : _int])))
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(mci-send-string "play sound.wav wait")}
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@desc{Using the FFI means that you're not limited to using Racket
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libraries: pulling out a foreign function is easy, and can even be done
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dynamically on the REPL.})
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;; Is this effective without any highlights?
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(generic-example ; -----------------------------------------------
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@code{#lang datalog
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ancestor(A, B) :- parent(A, B).
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ancestor(A, B) :-
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parent(A, C), D = C, ancestor(D, B).
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parent(john, douglas).
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parent(bob, john).
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ancestor(A, B)?}
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@desc{Racket is useful for building other languages. This example uses
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the pre-packaged Racket implementation of Datalog, a logic programming
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language. If you use this from DrRacket, you'll see that it provides
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proper highlighting, Check Syntax, and a Datalog-specific REPL.})
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#; ; Not easy to present something like this.
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(generic-example ; -----------------------------------------------
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@code{#lang racket
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(provide (except-out (all-from-out racket)
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#%top #%app)
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(rename-out [top #%top] [app #%app]))
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(define-syntax-rule (top . x) 'x)
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(define-syntax-rule (app f . xs)
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(if (hash? f) (hash-ref f . xs) (f . xs)))
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}
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@desc{TODO, and use this example:
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@pre{#lang s-exp "foo"
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(define x (make-hasheq))
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(hash-set! x A B)
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(x A)}})
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)))
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(define blurb "Racket is a programming language")
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(provide set-news-flashes!)
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(define news-flashes #f)
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(define (set-news-flashes! . text)
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(when news-flashes (error 'set-news-flashes! "text already set"))
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(set! news-flashes text))
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(provide index)
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(define index
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(page #:link-title "About" #:window-title "Racket"
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#:extra-headers @list{@meta[name: 'description content: blurb]
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@(lazy more.css)}
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@div[class: 'leftpane]{
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@span[style: "font-size: large; font-weight: bold;"]{Racket}
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is a programming language.
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@(and news-flashes (list br (div style: "width: 100%;" news-flashes)))}
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@div[class: 'downloadbutton]{@download-button}
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@div[class: 'aboutpane]{
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@div[class: 'panetitle]{Start Quickly}
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@div{@(apply slideshow-panel examples)}
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@p{@doc["quick/"]{Draw more pictures} or
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@doc["more/"]{build a web server from scratch}. Racket includes both
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@doc[""]{batteries} and a @doc["drracket/"]{programming environment},
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so @doc["getting-started/"]{get started}!}}
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@((λ xs (table class: 'threepanes
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(tr (map (λ (x) (td (div class: 'panetitle (car x)) (cdr x)))
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xs))))
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(list "Grow your Program"
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@p{Racket's
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@doc["guide/intro.html#(part._.Interacting_with_.Racket)"]{
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interactive mode}
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encourages experimentation, and quick scripts easily compose into
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larger systems. Small scripts and large systems both benefit from
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@doc["guide/performance.html"]{native-code JIT compilation}.
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When a system gets too big to keep in your head, you can add
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@doc["ts-guide/index.html"]{static types}.})
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(list "Grow your Language"
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@p{@doc["guide/languages.html"]{Extend Racket} whenever you need to.
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Mold it to better suit your tasks without sacrificing
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@doc["guide/dialects.html"]{interoperability} with existing
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libraries and without having to modify the
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@doc["guide/intro.html"]{tool chain}. When less is more, you can
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remove parts of a language or start over and build a new one.})
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(list "Grow your Skills"
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@p{Whether you're just @-htdp{starting out}, want to know more about
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programming language @-plai{applications} or @-redex{models},
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looking to @continue{expand your horizons}, or ready to dive into
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@learning{research}, Racket can help you become a better programmer
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and system builder.}))))
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(define (slideshow-panel l1 l2)
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(define l (append l1 l2))
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(define button-ids+labels '())
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;; this separator is shown in non-CSS browsers (eg, textual ones)
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(define invisible-separator @div[style: "display: none;"]{@br{}@hr{}})
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(define (button txt tip id onclick)
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(set! button-ids+labels (cons (cons id txt) button-ids+labels))
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(a href: "#" id: id onclick: (list onclick "; return false;") title: tip
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nbsp)) ; empty, filled by JS code, so JS-less browsers won't see it
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(div class: 'slideshow
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(div class: 'buttonpanel
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@button["<" "Previous example" 'rewindbutton "rewind_show()"]
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@button[">" "Next example" 'advancebutton "advance_show()"]
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@button["?" "Explain this code" 'helpbutton "set_help(!help_showing)"]
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(div class: 'hiddenhelp id: "helppanel" style: "display: none;"
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(div class: 'helpcontent
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@button["close" "Close help" 'closebutton "set_help(false)"]
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(div id: 'helpdesc "") ; placeholder for the descriptions (see below)
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@div[class: 'helptext]{
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Form and function names in the code are hyperlinked to
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documentation, so click on them for more information.})))
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(for/list ([elem (in-list l)] [pos (in-naturals)])
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@list{
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@invisible-separator
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@pre[class: 'slideshowframe id: @list{frame@pos}
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style: @list{display: @(if (zero? pos) "block" "none")@";"}]{
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@(example-code elem)}@;
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@; have the descriptions appear in a logical place and then ...
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@div[id: @list{helpframe@pos} style: "display: none;"]{
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@(example-desc elem)}})
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@invisible-separator
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@script/inline[type: "text/javascript"]{
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@; ... move them to a convenient-for-display place
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var helpdesc = document.getElementById("helpdesc");
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for (var i=0@";" i<@(length l)@";" i++) {
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var help_item = document.getElementById("helpframe"+i);
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help_item.parentNode.removeChild(help_item);
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helpdesc.appendChild(help_item);
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}
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var showing = 0, help_showing = false;
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var frame_s=new Array(), helpframe_s=new Array();
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for (var i=0@";" i<@(length l)@";" i++) {
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frame_s[i] = document.getElementById("frame" + i).style;
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helpframe_s[i] = document.getElementById("helpframe" + i).style;
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}
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var advbutton_s = document.getElementById("advancebutton").style;
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var rewbutton_s = document.getElementById("rewindbutton").style;
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function set_display(disp) {
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frame_s[showing].display = disp;
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helpframe_s[showing].display = disp;
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}
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function change_show_to(new_showing) {
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set_display("none");
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showing = new_showing;
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set_display("block");
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rewbutton_s.color = (showing==0) ? "#aaaaaa" : "#444444";
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advbutton_s.color =
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(showing==@(sub1 (length l))) ? "#aaaaaa" : "#444444";
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}
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function advance_show() {
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if (showing < @(sub1 (length l))) change_show_to(showing+1);
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}
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function rewind_show() {
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if (showing > 0) change_show_to(showing-1);
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}
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var help_panel_s = document.getElementById("helppanel").style;
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function set_help(show) {
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help_panel_s.display = show ? "block" : "none";
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help_showing = show;
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}
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change_show_to(Math.floor(Math.random() * @(length l1)));
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@; display button texts now, instead of making it part of the html,
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@; so it's not shown on JS-less browsers
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@(add-newlines
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(for/list ([id+label (in-list button-ids+labels)])
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(let ([id (car id+label)] [label (cdr id+label)])
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@list{document.getElementById("@id").textContent = "@label"@";"})))
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}))
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;; TODO
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;; (define screenshots
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;; (let ([image (copyfile (in-here "screenshot.jpg"))])
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;; @a[href: screenshots]{
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;; @img[src: image alt: "[screenshots]" border: 0
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;; style: "margin-bottom: 2px;"]@;
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;; @|br|@small{Screenshots}}))
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;; (define tour-video
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;; (page #:title "DrRacket Tour" #:file "tour.html"
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;; (define (center . body)
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;; (table align: 'center style: "margin: 3em 0em;"
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;; (tr (td align: 'center body))))
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;; ;; someone posted a comment saying that adding "&fmt=18" to the url
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;; ;; shows a higher resolution video, but it looks exactly the same.
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;; (define url "http://www.youtube.com/v/vgQO_kHl39g&hl=en")
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;; @center{
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;; @object[type: "application/x-shockwave-flash" data: url
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;; width: (round (* 3/2 425)) height: (round (* 3/2 344))]{
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;; @param[name: "movie" value: url]}}))
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;; resources that are specific to the front page
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(define loud (copyfile (in-here "loud.png")))
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(define more.css
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@plain[#:referrer (λ (url) (link rel: "stylesheet" type: "text/css"
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href: url title: "default"))]{
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.bodycontent {
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background-image: url('@loud');
|
||
background-repeat: no-repeat;
|
||
background-position: center top;
|
||
}
|
||
.leftpane {
|
||
font-size: medium;
|
||
float: left;
|
||
width: 20%;
|
||
}
|
||
.aboutpane {
|
||
width: 56%;
|
||
margin-right: auto;
|
||
margin-left: auto;
|
||
}
|
||
.panetitle {
|
||
width: 100%;
|
||
font-size: large;
|
||
font-weight: bold;
|
||
color: #dd0000;
|
||
}
|
||
.threepanes {
|
||
width: 100%;
|
||
}
|
||
.threepanes td {
|
||
vertical-align: top;
|
||
margin: auto;
|
||
width: 30%;
|
||
padding: 0.5em;
|
||
}
|
||
.slideshow {
|
||
position: relative;
|
||
}
|
||
.slideshowframe {
|
||
height: 17ex;
|
||
}
|
||
.buttonpanel {
|
||
display: block;
|
||
position: absolute;
|
||
left: 100%;
|
||
top: -3ex;
|
||
width: 3em;
|
||
margin: 0em 0em 0em -5em;
|
||
}
|
||
#advancebutton, #rewindbutton, #helpbutton, #closebutton {
|
||
text-decoration: none;
|
||
border: 1px solid #ddddd;
|
||
font-weight: bold;
|
||
color: #44444;
|
||
background-color: #eeeee;
|
||
padding: 0px 1px 0px 1px;
|
||
}
|
||
#advancebutton, #rewindbutton {
|
||
margin: 0px 1px 0px 1px;
|
||
}
|
||
#helpbutton {
|
||
margin: 0px 1px 0px 10px;
|
||
}
|
||
.hiddenhelp {
|
||
width: 0em;
|
||
margin-left: 2em;
|
||
}
|
||
.helpcontent {
|
||
width: 20em;
|
||
background-color: #ffffee;
|
||
padding: 10px;
|
||
margin-top: 3px;
|
||
border: 1px solid black;
|
||
}
|
||
#closebutton {
|
||
font-size: small;
|
||
margin-bottom: 1em;
|
||
}
|
||
.helptext, #helpdesc {
|
||
margin-top: 0.5em;
|
||
}
|
||
.helptext {
|
||
font-size: small;
|
||
}
|
||
.downloadbutton {
|
||
position: relative;
|
||
float: right;
|
||
}
|
||
@;
|
||
.codecomment {
|
||
color: #c2741f;
|
||
}
|
||
.codeparenthesis {
|
||
color: #843c24;
|
||
}
|
||
.codeconstant, .codestring {
|
||
color: #228b22;
|
||
}
|
||
.codeid, .codemodpath {
|
||
color: #262680;
|
||
}
|
||
.codeimportid {
|
||
color: blue;
|
||
}
|
||
.codeimportform {
|
||
font-weight: bold;
|
||
}
|
||
.codelinkimportid {
|
||
color: blue;
|
||
text-decoration: none;
|
||
}
|
||
.codelinkimportform {
|
||
font-weight: bold;
|
||
color: black;
|
||
text-decoration: none;
|
||
}
|
||
.codelinkimportid:hover {
|
||
text-decoration: none;
|
||
}
|
||
.codelinkimportform:hover {
|
||
text-decoration: none;
|
||
}
|
||
.codemodpath:hover {
|
||
text-decoration: none;
|
||
}})
|