Jens Axel Søgaard soegaard

The introduction to Reactive Programming you've been missing

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

Install Nginx on Mac OS from source

no Homebrew required

1. Download Nginx

$ cd /usr/local/src
$ curl -OL http://nginx.org/download/nginx-1.12.2.tar.gz
$ tar -xvzf nginx-1.12.2.tar.gz && rm nginx-1.12.2.tar.gz

Racket tips and tricks

These are extracted from discussions I triggered on the Racket Slack. Thanks to everyone who participated in the discussion threads! :-)

Conversion to boolean

Use (and value #t) to convert a value to its boolean equivalent.

Entering a module in the Racket REPL

Primality tests like the Fermat test and the Miller-Rabin test rely on so-called "witnesses." In the case of Fermat, if a^{p-1} = 1 (mod p), for some a, then p is probably prime. The a is called a Fermat witness. However, if a composite passes the test for a given a, then a is called a Fermat liar. The same principle holds for Miller-Rabin, although the equation is slightly more complicated.

Which numbers are the most honest? Which ones are the most lying? Run racket main.rkt to produce a bunch of heat maps that show the most honest (dark) and most lying (bright) numbers. This one shows for the numbers 2 to 1024:

	;SMBDIS.ASM - A COMPREHENSIVE SUPER MARIO BROS. DISASSEMBLY
	;by doppelganger ([email protected])

	;This file is provided for your own use as-is. It will require the character rom data
	;and an iNES file header to get it to work.

	;There are so many people I have to thank for this, that taking all the credit for
	;myself would be an unforgivable act of arrogance. Without their help this would
	;probably not be possible. So I thank all the peeps in the nesdev scene whose insight into
	;the 6502 and the NES helped me learn how it works (you guys know who you are, there's no

	{
	// Evaluate file in the open SublimeREPL.
	// Depends on you creating the Packages/User/EvalInREPL.sublime-macro file.
	{ "keys": ["super+r"], "command": "run_macro_file", "args": { "file": "Packages/User/EvalInREPL.sublime-macro" },
	"context": [
	{ "key": "selector", "operator": "equal", "operand": "source.elm" }
	]
	},

	// Reindent selection on tab

	#lang racket
	(require json racket/draw math/base)

	(define (lat-lon->map-point coordinates)
	(match-define (list lon lat _ ...) coordinates)
	(define-values (x y) (values (degrees->radians lon) (asinh (tan (degrees->radians lat)))))
	(list (/ (+ 1 (/ x pi)) 2) (/ (- 1 (/ y pi)) 2)))

	(define (draw-polygon dc polygons)
	(define path

	#lang sketching
	(require racket/list)

	(class Player Object
	(init-field x y x-vel y-vel attached)
	(super-new)

	;direction is whether we're rotating clockwise or anti clockwise around the ball.
	;either -1 or 1
	(define-values (direction) (values 1))

	#lang racket
	(require math/array)
	;; https://en.wikipedia.org/wiki/Conway's_Game_of_Life

	;; These are the game rules for a single CELL which can be 1 (alive) or 0
	;; dead. NEIGHBOR-COUNT is the number of live neighbors the cell has.
	(define (game-rules cell neighbor-count)
	(cond
	;; Any live cell with fewer than two live neighbours dies, as if by
	;; underpopulation.