Farley Knight farleyknight

Clojure Destructuring Tutorial and Cheat Sheet

Simply put, destructuring in Clojure is a way extract values from a datastructure and bind them to symbols, without having to explicitly traverse the datstructure. It allows for elegant and concise Clojure code.

Vectors and Sequences

Provider	Singleton	Instantiable	Configurable
Constant	Yes	No	No
Value	Yes	No	No
Service	Yes	No	No
Factory	Yes	Yes	No
Decorator	Yes	No?	No
Provider	Yes	Yes	Yes

Constant

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

	import sys; from PIL import Image; import numpy as np

	chars = np.asarray(list(' .,:;irsXA253hMHGS#9B&@'))

	if len(sys.argv) != 4: print( 'Usage: ./asciinator.py image scale factor' ); sys.exit()
	f, SC, GCF, WCF = sys.argv[1], float(sys.argv[2]), float(sys.argv[3]), 7/4

	img = Image.open(f)
	S = ( round(img.size[0]SCWCF), round(img.size[1]*SC) )
	img = np.sum( np.asarray( img.resize(S) ), axis=2)

	# Based on http://cr.yp.to/streamciphers/timings/estreambench/submissions/salsa20/chacha8/ref/chacha.c

	import binascii
	import numpy as np

	np.seterr(over='ignore')

	def rotl32(v, c):
	assert isinstance(v, np.uint32)
	assert isinstance(c, np.uint32)

	source :rubygems

	gem 'json', '= 1.5.4' # knife/chef 11.0 and 11.20 is broken with json 1.5.5/1.7.7
	gem 'vagrant'
	gem 'vagrant-hostmaster'

	<!DOCTYPE html>
	<html>
	<head>
	<title>Capture Photo</title>
	<meta name="viewport" content="width=device-width,height=device-height,initial-scale=1"/>
	<script type="text/javascript" charset="utf-8" src="js/phonegap.js"></script>
	<script type="text/javascript" charset="utf-8">

	var pictureSource; // picture source
	var destinationType; // sets the format of returned value

	// node:
	var moment = require('moment');

	moment().add('days', 2).fromNow();
	// 'in 2 days'

	moment().subtract('days', 2).fromNow();
	// '2 days ago'

	moment('November 1977').fromNow()

	/**
	* C++ property implementation
	* Christoph Heindl 2011
	* [email protected]
	*/

	#pragma once

	#include <cheind/properties/property.h>
	#include <cheind/properties/policy_optional_value.h>