Raimon Grau kidd

Sessions and Conversations

HTTP is a stateless protocol. Sessions allow us to chain multiple requests together into a conversation between client and server.

Sessions should be an option of last resort. If there's no where else that the data can possibly go to achieve the desired functionality, only then should it be stored in the session. Sessions can be vulnerable to security threats from third parties, malicious users, and can cause scaling problems.

That doesn't mean we can't use sessions, but we should only use them where necessary.

Adding, Accessing, and Removing Data

Partial Evaluation, Futamura Projection And Their Applications

What Partial Evaluation Is?

Partial evaluation means to fix some variables in the given code before execution. With a traditional implementation of a compiler or an interpreter, all variables are replaced with its value on each evaluation of that variable. This is because a variable can change at any timing. This is, however, not always true in actual applications. Almost all of large applications has setting variables and data

Business Models

Advertising

Models	Examples
Display ads	Yahoo!
Search ads	Google

Hofstadter on Lisp

In the mid-80s, while reading through my roommate's collection of Scientific American back issues, I encountered this introduction to Lisp written by Douglas Hofstadter. I found it very charming at the time, and provide it here (somewhat illegally) for the edification of a new generation of Lispers.

In a testament to the timelessness of Lisp, you can still run all the examples below in emacs if you install these aliases:

(defalias 'plus #'+)
(defalias 'quotient #'/)
(defalias 'times #'*)
(defalias 'difference #'-)

	(defpackage :brainfuck (:use :cl))

	(in-package :brainfuck)

	(defun string->brainfuck (source)
	(let* ((fragments
	(map 'list
	(lambda (c)
	(case c
	(#\> "(incptr 1)")

	#!/usr/bin/perl
	#
	#
	# This perl script is dumping the urls submitted
	# by an HN user. Sometime it's better than any
	# del.icio.us stream when the HN user has some
	# special interests.
	#
	# Usage:
	#

	URxvt*termName: rxvt-256color
	URxvt*xftAntialias: true
	URxvt*background: #3f3f3f
	URxvt*foreground: #dcdccc
	URxvt*cursorColor: #aaaaaa
	URxvt*colorUL: #366060
	URxvt*underlineColor: #dfaf8f
	URxvt*color0: #3f3f3f
	URxvt*color1: #cc9393
	URxvt*color2: #7f9f7f

	#!/usr/bin/env ruby

	def pop; $stack.pop \|\| raise(StackUnderflow); end
	def push(expression); $stack << expression; end
	def unary; -> { push(yield pop) }; end
	def binary; -> { push(yield pop, pop) }; end
	def unary_boolean; -> { push(if yield pop then 1 else 0 end) }; end
	def binary_boolean; -> { push(if yield pop, pop then 1 else 0 end) }; end
	def swap; $stack[-2,2] = $stack[-2,2].reverse; end
	$stack = []

	if not sinatra.incoming ( ngx.req.get_method() , ngx.var.uri ) then
	return ngx.exit ( 404 )
	end