(require 2htdp/image) ; draw a picture
(let sierpinski ([n 8])
  (cond
    [(zero? n) (triangle 2 'solid 'red)]
    [else (define t (sierpinski (- n 1)))
          (freeze (above t (beside t t)))]))

The 2htdp/image library provides easy-to-use functions for making images.

Racket tutorial →

@; Generate a PDF or HTML document
@title{Bottles: @italic{Abridged}}
@(apply
  itemlist
  (for/list ([n (in-range 100 0 -1)])
    @item{@(format "~a" n) bottles.}))

The scribble/base language generates documents using a prose-friendly syntax.

Scribble tutorial →

;; Using higher-order occurrence typing
(define-type SrN (U String Number))
(: tog ((Listof SrN) -> String))
(define (tog l)
  (apply string-append (filter string? l)))
(tog (list 5 "hello " 1/2 "world" (sqrt -1)))

Typed Racket’s “gradual” typing lets you add types after you’ve been working in untyped mode.

Typed Racket tutorial →

ancestor(A, B) :- parent(A, B).
ancestor(A, B) :-
  parent(A, C), ancestor(C, B).
parent(john, douglas).
parent(bob, john).
ancestor(A, B)?

You can use Racket to build other languages — like datalog, a logic-programming language.

Datalog tutorial →

(define f (new frame% [label "Guess"]))
(define n (random 5)) (send f show #t)
(define ((check i) btn evt)
  (message-box "." (if (= i n) "Yes" "No")))
(for ([i (in-range 5)])
  (make-object button% (~a i) f (check i)))

Racket’s GUI language and libraries makes cross-platform applications easy.

GUI tutorial →

;; A "hello world" web server
(define (start request)
  (response/xexpr
   '(html
     (head (title "Racket"))
     (body "Hello World"))))

The web-server/insta language lets you quickly prototype server-side web applications.

Web-application tutorial →