Trying to find exceptions in Haskell

In my quest to re-learn Haskell I eventually thought: “OK, let’s see how an exception looks like”. Starting my favorite interactive Haskell implementation:

   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.4.1, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base-1.0 ... linking ... done.
Prelude>

OK. Let’s generate an exception now, a division by zero for example (something basic): Continue reading “Trying to find exceptions in Haskell”

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Django… awesome

I have an idea for a web application that might enjoy moderate success. And from time to time I try to develop it and it would be already done if it wasn’t that web developing is so painful (reading PLAI and trying to make my own Lisp to conquer the word is far more fun and entretaining… oh damn, I shouldn’t told you my plan… oh well).

My favourite framework so far is (and continues to be, more on that latter): UnCommon Web (UCW). But after reading an article titled Framework Performance (or Django vs. Rails vs. Symfony: Django is fastest on digg) I said: “Hey, let’s give this Django thing a try”.

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The lambda revolution, Episode V, the deb strikes back

There’s an excellent article by Don “dons” Stewart called The lambda revolution which explains how to build a Haskell library in way that it is easy to download, compile, install, test, distribute, etc. I believe all those qualities are essential for successfully software. The next logicall step is to make OS-specific packages of it and since today I’ve had a short talk with Ian “Iglo” Lynagh, maintainer of many Haskell packages on Debian, who dissipated all my doubts about how to build a deb package of a Haskell library. Armed with that knowledge I am going to turn Don’s dlist into a beautiful deb package for Debian, Kubuntu or any other deb based operating system and tell you how.
Continue reading “The lambda revolution, Episode V, the deb strikes back”

Cleaning up a Debian GNU/Linux (or Ubuntu), reprise

My little article Cleaning up a Debian GNU/Linux was published at Debian Administration where lot’s of people replied with other ways to achieve the same goals. It was very nice to see all the different approaches with all the different pros and cons.

In the end I ended up changing my own approach for one that is faster and cleaner so I wanted to share it with you. Still, go to the Debian Administration version of the article and read the comments, they are very cool (thanks to all those who posted!).

Continue reading “Cleaning up a Debian GNU/Linux (or Ubuntu), reprise”

Cleaning up a Debian GNU/Linux

You arrive at a Linux server which has some history of neglect. Let’s suppose someone else neglected it but if your new-year resolution is to stop neglecting your beloved server, this applies as well.

One form of neglect is to install, install, install and never un-install any package. The common utility to perform installation and un-installation of packages is apt-get which adds to the problem because it doesn’t have automatic removal of non-needed dependences.

PHP and ton of other packages. phpMyAdmin was removed when it was no longer needed but Apache, PHP and the ton of packages remain there.

Aptitude to the rescue. Aptitude is another package manager front-end like apt-get but it can keep track of automatically and non-automatically installed packages. That means that when you installed phpMyAdmin it was marked as non-auto while Apache and company was marked as auto. When you remove phpMyAdmin all the non-needed automatically installed packages like Apache would be removed.

Continue reading “Cleaning up a Debian GNU/Linux”

Erlang, the language for network programming Issue 2: binary pattern matching

Much is being said about the excellent capabilities of Erlang to write distributed fault-tolerant programs, but little has been said about how easy and fun it is to write servers (those programs at the other end of the line) with it. And by easy I don’t just mean that you can put up a web server in two lines of code and hope it’ll work, I mean it’ll be easy to built robust servers.

One example of this is ejabberd, a free Jabber server.

I’ll start this second part, the one with real networking programming, with a bet. Think about the IPv4 protocol, its header is like this:

0                   1                   2                   30
  1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version|  IHL  |Type of Service|          Total Length         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Identification        |Flags|      Fragment Offset    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Time to Live |    Protocol   |         Header Checksum       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Source Address                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Destination Address                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Options                    |    Padding    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

you can check RFC791, page 11 for more information. At a glance, the first 4 bits are the version, the next 4 bits the IHL (Internet Header Length), then we have a whole byte, 8 bits, of Type of Service. The next two bytes are the total length and I am already tired of it, you get the picture right?

Pick whatever language you want (except Erlang, that’s mine now, but it can be yours latter) and think about how many lines of code would take you to parse that beast, the IP header. Think about how much time it takes you to write those lines, and test them.

Done? come on! really think about it, otherwise the game is boring. Close your eyes, picture the lines of code. If you can’t, go and write some pseudo-code similar to your favorite language to do the parsing. Done? OK.

Here’s my bet: I bet that I can do it, in Erlang, in far less lines than you! I bet you that I can code it so fast that I’d be finished of writing the code to parse the whole header before you finish the code to parse the first line. And while you are testing I’ll go to the beach because I’ll just trust my code to run without problems.
Continue reading “Erlang, the language for network programming Issue 2: binary pattern matching”

Erlang, the language for network programming Issue 1: pattern matching

Much is being said about the excellent capabilities of Erlang to write distributed fault-tolerant programs, but little has been said about how easy and fun it is to write servers (those programs at the other end of the line) with it. And by easy I don’t just mean that you can put up a web server in two lines of code and hope it’ll work, I mean it’ll be easy to built robust servers.

One example of this is ejabberd, a free Jabber server.

One of the Erlang features that let us write servers is its binary pattern matching. But to understand binary pattern matching first you have to understand pattern matching.

Let’s start with a classic of functional programming: factorial. This is factorial in Erlang

fac(N) ->
   if N == 0 -> 1;
      true -> N * fac(N - 1)
   end.

Continue reading “Erlang, the language for network programming Issue 1: pattern matching”

Software Release Cycle

Introduction

I am writing this description to remember what to do when I reach the time to release one of my various projects1, that doesn’t happen often enough for me to remember the whole process and it is tedious enough to hate it when I forget a step. So, I decided to describe it.

First I will explain the version numbers I use. At one time I used the Linux version numbers but when I worked in KDE I’ve seen the beauty of their version numbers (if there’s place for beauty in such a thing).

Then I’ll explain how I create and maintain the various branches, tags and tarballs.
Continue reading “Software Release Cycle”