# 200!

*posted by Asumu Takikawa*

About a month ago, inspired by a mailing list post by Tim Brown, Racketeers started to write more solutions to Rosetta Code tasks for Racket. Just today, we’ve reached 200 entries in the Racket category!

This is a nice milestone, but we still have a ways to go. At 200 entries, Racket comes in at around 54th in the popularity rankings. So if you’re looking to practice your Racketeering skills, don’t hesitate to work on some of the remaining tasks.

To give you a taste of the kinds of solutions we have so far, here are some examples.

Mandelbrot:

(define (iterations a z i) (define z′ (+ (* z z) a)) (if (or (= i 255) (> (magnitude z′) 2)) i (iterations a z′ (add1 i)))) (define (iter->color i) (if (= i 255) (make-object color% "black") (make-object color% (* 5 (modulo i 15)) (* 32 (modulo i 7)) (* 8 (modulo i 31))))) (define (mandelbrot width height) (define target (make-screen-bitmap width height)) (define dc (new bitmap-dc% [bitmap target])) (for* ([x width] [y height]) (define real-x (- (* 3.0 (/ x width)) 2.25)) (define real-y (- (* 2.5 (/ y height)) 1.25)) (send dc set-pen (iter->color (iterations (make-rectangular real-x real-y) 0 0)) 1 'solid) (send dc draw-point x y)) target) > (mandelbrot300200)

Yin and Yang:

(define (yin-yang d) (define base (hc-append (inset/clip (circle d) 0 0 (- (/ d 2)) 0) (inset/clip (disk d) (- (/ d 2)) 0 0 0))) (define with-top (ct-superimpose base (cc-superimpose (colorize (disk (/ d 2)) "white") (disk (/ d 8))))) (define with-bottom (cb-superimpose with-top (cc-superimpose (disk (/ d 2)) (colorize (disk (/ d 8)) "white")))) (cc-superimpose with-bottom (circle d))) > (yin-yang 200)

Animate a pendulum:

#lang racket (require 2htdp/image 2htdp/universe) (define (pendulum) (define (accel θ) (- (sin θ))) (define θ (/ pi 2.5)) (define θ′ 0) (define θ′′ (accel (/ pi 2.5))) (define (x θ) (+ 200 (* 150 (sin θ)))) (define (y θ) (* 150 (cos θ))) (λ (n) (define p-image (underlay/xy (add-line (empty-scene 400 200) 200 0 (x θ) (y θ) "black") (- (x θ) 5) (- (y θ) 5) (circle 5 "solid" "blue"))) (set! θ (+ θ (* θ′ 0.04))) (set! θ′ (+ θ′ (* (accel θ) 0.04))) p-image)) (animate (pendulum)) Jensen's Device: ```racket #lang algol60 begin integer i; real procedure sum (i, lo, hi, term); value lo, hi; integer i, lo, hi; real term; comment term is passed by-name, and so is i; begin real temp; temp := 0; for i := lo step 1 until hi do temp := temp + term; sum := temp end; comment note the correspondence between the mathematical notation and the call to sum; printnln (sum (i, 1, 100, 1/i)) end

Thanks to all of the people who have contributed solutions so far!