Jack Rusher jackrusher

Object-orientation

There are many articles and discussion threads on the web regarding the nature of Object-oriented (OO) programming. Most of them come at the question from a Programming Language Theory (PLT) perspective, attempting to assert a formal definition of OO programming and objects. I'm not going to do that here. Instead, I'm going to write about objects from an implementation perspective, approaching the subject first from below and then from above.

Functions, how do they work?

A good friend asked me how functions work under the covers, so I wrote up this quick explanation. Corners are cut for brevity, but I hope it will convey the general idea.

The three assembly language programs below implement the following (super simple) recursive function:

	# lightweight processing-esque canvas wrapper
	class Sketch
	constructor: (width, height) ->
	@running = false
	@canvas = (document.getElementsByTagName 'canvas')[0]
	if @canvas
	@canvas.parentNode.removeChild @canvas
	@canvas = document.createElement 'canvas'
	@canvas.width = width
	@canvas.height = height

	;;; skewer-coffee.el --- skewer support for live-interactive Coffeescript

	(defun skewer-coffee-eval (coffee-code)
	"Requests the browser to evaluate a coffeescipt string."
	;; XXX should escape double quote characters
	(skewer-eval (concat "CoffeeScript.eval(\""
	(s-replace "\n" "\\n" (s-trim coffee-code))
	"\");")
	#'skewer-post-minibuffer))

	(ns workbook.euclid
	(use quil.core))

	(defn hex-to-dec
	"Convert hex RGB triples to decimal."
	[s]
	(map (comp #(Integer/parseInt % 16) (partial apply str))
	(partition 2 s)))

	(defn hex-stroke

	;; follows redirects
	(defn fetch-page [url]
	(enlive/html-resource
	(loop [final-url (java.net.URL. url)]
	(let [conn (.openConnection final-url)]
	(if (re-find #"30[1-3]" (.getHeaderField conn 0))
	(recur (java.net.URL. (.getHeaderField conn "location")))
	final-url)))))

	;; grab page title string

	(ns blue-ball
	(:use [seesaw core font graphics])
	(:require [clojure-leap.core :as leap]
	[clojure-leap.screen :as l-screen]))

	;; these atoms contain the current x/y state from the Leap
	(def x (atom 10))
	(def y (atom 10))

	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Build the window/canvas

	(ns leap-quil-cube
	(:require [clojure-leap.core :as leap]
	[clojure-leap.hand :as hand]
	[clojure-leap.screen :as screen]
	[clojure-leap.vector :as v]
	[clojure-leap.pointable :as pointable :refer [tip-position]])
	(:use quil.core))

	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Quil cube

	(def legal-char (set (map char (concat (range 48 58) (range 97 123)))))

	(defn tokenize [s]
	(->> (map-indexed list (string/lower-case s))
	(partition-by (comp not legal-char second))
	(filter (comp legal-char second first))
	(mapv #(hash-map :s (apply str (map second %))
	:begin (first (first %))
	:end (first (last %))))))

	(defrel triple ^{:index true} s ^{:index true} p ^{:index true} o)

	(facts triple [[:Berlin :is-a :city]
	[:city :is-a :permanent-settlement]
	[:Berlin :part-of :Germany]
	[:Germany :part-of :EU]
	[:EU :part-of :Eurasia]
	[:Eurasia :part-of :Earth]])

	(run* [q] (triple q :is-a :city))