Categories
Programming

Language of the Month: Javascript

Continuing the Language of the Month serious after a little bit of break when I was busy with other stuff:

Javascript icon
Just a Javascript icon...

It is very long overdue, since I was looking at Javascript like…. 14 years now? But never really spent time to understand it because I never needed it really. I’m old enough to remember that when I started to browse the web, every time there was a page using Javascript, people’s sentiment was “oh, no, that’s going to be very slow, I don’t even want to check this site anymore”. Pretty much like it was/is with Flash later on.

Compare this to now, how 100% static sites are practically disappeared, and no web developer worth their salt should skip on learning it. I’m glad that browsers spent a lot of time improving performance and that so many interesting projects came out of it.

My impression of the current state of the art is that using HTML + CSS + Javascript now it is easier than ever to make good front-ends for programs. I’m mostly a command-line guy (and that’s pretty easy with many scripting languages as well as Python that I use), but I cannot deny that I’m the minority. Still, when i need convenience, I can even imagine people creating local (meaning not internet-enabled) software with those things.

Since more and more people had similar idea and started to work on it, there are plenty of projects that make this even easier, like jQuery and all its plugins. I don’t think people need a lot of introduction and already can do a lot of things easier using that. One drawback is that many things could be just as easily done in pure Javascript but people quite often don’t know that. I certainly have to learn a lot more.

In this month I was reading a few books and sites that people recommended on Hacker News, as well as I used it to do a few actual projects. Now that’s a change compared to the previous Language of the Month columns.

Projects

WatchDoc: a Chrome extension that notifies you when your shared documents on Google Docs change. Chrome extensions are merely HTML+CSS+JS code, so it was a perfect way to try a few things. (Will write it up here later) (wrote up here).

NowJS real time games hackathon: NowJS is a real-time communication plugin for NodeJS, the JS server. I wanted to make a game for this hackathon, but run out of time. Spent some time working with it, and it’s actually pretty awesome when I started to understand it, I’m do want to finish the game at a later time (it’s a multiplayer trivia game) . (Will write it up here later)

Venus & Mars: a little afternoon project using Facebook to help my friend’s research assignment at her university. Listing people’s status updates separated by gender. It looks awfully ugly, because I just wanted to make it work, but for the fun of it it’s NodeJS so good to practice my JS-foo.  (Will write it up here later)

Impressions

I definitely going to learn more of it, because now that I start to understand I quite like it, and I cannot imagine it going away anytime soon. Now that it is just a matter of seconds to set up a project on the web (really, on Heroku, Appengine, dotCloud are all one click away) there’s no good excuse not to do that.

Good

  • JSON, ’nuff said. That’s just such a good data format that is both human and machine readable. Seem to be pretty much the
  • No problem (it seems) with Unicode and international characters. Though I think it uses UTF-16 while many other code is using UTF-8, not sure if that makes any difference.
  • Feels quite light and flexible (from the language point of view, not necessarily the resources needed)
  • Since the source of websites is necessarily open, it is possible to learn from others’ examples much easier than otherwise.

Bad

  • Feels like it has a lot of baggage from it’s long(ish) and torrid life, which makes it feel a bit inconsistent. E.g. the first day of the month is 1, but the first month (January) is 0.
  • People generally seem to write pretty bad Javascript code. Because it’s so easy everyone can make some useful project, but they are full of bugs. Fortunately it’s Open Source, so I can try to figure it out, and I did find a handful of upstream bugs. But the stress…. huh…

Ugly

  • Formatting of JS code can be pretty unreadable (especially comparing with Python where formatting is not optional). It is made more difficult when I’m editing JS within a HTML file, since Emacs cannot handle that well.
  • Up until quite recently there weren’t any really good tools to troubleshoot things. Fortunately there’s Chrome and it’s Javascript console, and Firebug for Firefox. There are still some mysterious errors and the debugging has to be planned well ahead.
  • There are many things that are straightforward but require a lot of typing. Fortunately projects like jQuery are trying to fix that, but still there’s a long way to go.
  • Just like in Lua, for keys in dictionaries the quotation marks are not required and they are still understood as strings. These kind of magic can be convenient but there are occasions when confusing.

Links

Books

Interesting Javascript projects and sites

  • jQuery: making it easier to use JS, especially with respect to HTML DOM manipulation
  • Node.js: server side JS, thus it is possible for the first time (?) to use the same language for the front and back end on the web
  • jsFiddle: easy online editor, prototyping and code sharing for the web (JavaScript, MooTools, jQuery, Prototype, YUI, Glow and Dojo, HTML, CSS)

(last edited 2011-10-03)

Categories
Programming

Language of the Month: Prolog, part 2

If something, then this is a belated post. Prolog was the language of July and now it’s September. Anyway, before I completely fail, let’s just wrap it up and go on the next language with this one month hiatus in August.

I really enjoyed the language and one month is indeed barely enough to start doing something useful. So I have to come back to it again and maybe keep reading about it in the meantime. It’s actually quite interesting to try to figure out Prolog code on paper, without actually running something. I think one of the books I was reading had plenty of exercises like this: without running the code, can you guess what is it doing? Needless to say, there were plenty of tricky bits/

From the comments

During two months, some additional resources did show up. A dear commenter on the previous post recommended me the following book: Richard O’Keefe: The Craft of Prolog. I got about a third, maybe halfway through it and it’s interesting, written long time ago in a style that since gone out of fashion, unfortunately. It’s a programming book that is fun to read and one can see that the author is very knowledgeable. Some aspects of the book didn’t age very well, though. The author keeps comparing Prolog to other languages – many of them are not very widely available either. Also, some of the language features are specific to his version of Prolog, that wasn’t the same one I was using. Would recommend, though!

This last part, the different implementations of the same language, can be a real problem. Of the three compilers available for me, all of them had specific strengths and weaknesses. Guess they are converging, but not quite yet. So far I was mostly using SWI Prolog, but this might change in the future.

The said commenter also recommended a cross-compiler, doing Prolog-to-C magic, for portability and other goodness. Can grab it from here: http://ftp.shaw.ca/irvinsh/prolog.tar.gz I haven’t had time to try it yet, but once I have, I’ll do a comparison.

From the web

From a friend’s recommendation I was checking out a site with free textbooks. They are all advertisement-sponsored, which is an intriguing idea (for another post). The IT section had not one but two books on Prolog: Prolog Techniques and Applications of Prolog.

Two prolog book covers
Free textbooks on Prolog from Bookboon

This latter one has a Hungarian author so I’m even more intrigued, we used to have great computer scientists (John von Neumann / Neumann János, anyone?), so I hope we keep up that tradition. (Oh, yeah, and had great physicists as well, maybe I can do more on that front later).

I was only skimmed them a little bit, but looks like these will be good addition for my “programming for fun and efficiency” library.

Will update the original LotM:Prolog page with these links as well. Now onto September’s Language, fortunately I have idea what I want to learn for the next ~3.5 weeks. October will be something Artificial Intelligence related since I signed up for the AI-class.

Categories
Programming

Language of the Month: Prolog

New month, new programming language to learn, the 3rd one in this series. So the repertoire so far contains:

Prolog

It is again a very different choice, logic programming. Been playing with it for the last two weeks or so, and it really makes me think differently about programming and programs. Logic and complex thinking was always a favorite past-time of me (e.g. solving puzzles and such), but only now I realized that I do have a lot to practice in this area.

Prolog is also one of the older languages (feels like a “classmate” of Lisp and Fortran) so it was the first language in the series where I could actually go to a library, take out some books to learn it, and that book wasn’t hopelessly out of date (try to do the same thing with Python or Ruby…). Since these books were also written by academics and not necessarily computer scientists, their whole approach is different, in a way more curious, though probably less practical.

In the end, I think what I would like to gain is a tool that I can use to attack problems that are intractable or at least very difficult in other languages.

Start

One of the first thing I found hard to figure out was how to actually run a program. So in a nutshell: even if most of the interaction is within an interpreter-like environment, all the basics have to be prepared in a file and loaded.

E.g. I prepare a file like this (based on Ender’s Game), call it ender.pl:

%% Genealogy of Ender's Game.
% Facts
male(ender).
male(peter).
male('john paul').
female(valentine).
female(theresa).

parent('john paul', ender).
parent('john paul', peter).
parent('john paul', valentine).
parent(theresa, ender).
parent(theresa, peter).
parent(theresa, valentine).

% Predicates
father(X, Y) :-
	male(X),
	parent(X, Y).
mother(X, Y) :-
	female(X),
	parent(X, Y).

sibling(X, Y) :-
	father(F, X), mother(M, X),
	father(F, Y), mother(M, Y),
	X \= Y.
brother(X, Y) :-
	male(X),
	sibling(X, Y).
sister(X, Y) :-
	female(X),
	sibling(X, Y).

Then starting Prolog I can load the file with the [‘ender.pl’]. form, and ask questions like who is Ender’s sister? Who are Theresa’s kids? Who are Peter’s siblings?

?- ['ender.pl'].
% ender.pl compiled 0.00 sec, 144 bytes
true.

?- sister(Sis, ender).
Sis = valentine ;
false.

?- mother(theresa, Kid).
Kid = ender ;
Kid = peter ;
Kid = valentine.

?- sibling(peter, X).
X = ender ;
X = valentine ;
false.

Well, this is laughably simple, and I’m beyond this already, but it’s good for a first illustration.

By the way, it looks like 90% of elementary Prolog examples use family trees (Nordic or Greek gods, literary, real families…)

Now let’s get in there and learn some more stuff…

Links

Tutorials & Info

Books

Compilers

Code

Categories
Programming

Language of the Month: Lua, part 2

I’m a few days behind schedule since Lua was June’s language, but here it comes, some summary of my experience, after setting things up in the first part.

A Trip to the Moon / Le Voyage dans la Lune
Lua is not this painful, indeed, just the opposite

Overview

I really liked this language, and I’m sure I’ll keep learning it. Very useful and lots of interesting concepts. I haven’t seen an embedded language before, and some parts

Most of what I picked up was from Beginning Lua Programming and Programming in LuaLua Missions was another very useful experience: a “fill in the blank” type of source code collection, which drilled my understanding of the Lua concepts. Some sections felt a little short, so maybe later I’ll think whether there are any more questions I can come up with. Very well worth the time!

There are two things that stand out: tables and local environments.

Tables

If I have to refer to my knowledge of Python, then Lua tables are like Python lists and dicts rolled into one and then some. Here’s one such table:

x = {1, 2, 3, y = "something", ["or else"]="what"}

The first three elements are giving an array (and one can loop over them), then the last two are key-value pairs. One tricky thing is that the “y” there is actually a string (the same as [“y”]), just made it more readable with syntactic sugar. Since variables (references to variables) can be keys as well, this can get confusing if one has a variable called “y”… There are quite a few things about tables that are confusing, but actually pretty consistent so my fuses are not blowing that much as they were in the beginning (for example: how the length is looked up, how to iterate through the different values) .

They are very complex animals so some things are quite complex to do, which in turn enables quite complex things to be done. Pretty much any kind of data structure can be built upon them. So all in all, I’m enjoying them with all their quirks. Also, “weak tables” are an interesting concept (where certain table entries can garbage collected).

Scopes

In Python, the name spaces and environments seem to be on the sidelines (at least what I’ve seen so far): people need it and have to us it, but nothing more than that. In Lua this is taken to a whole new level: scopes can be essential parts of the way algorithms are implemented and neat tricks can be played.

I tried to come up with some good example and failed, here’s a “duh” one:

function newCounter ()
    local i = 0
    return function ()   -- anonymous function
        i = i + 1
        return i
    end
end

c1 = newCounter()
print(c1())  -- 1
print(c1())  -- 2

This is a bit like Python’s “yield” type of generator, without anything special.

Also, in Python there are only two kinds of variables (I think): local and global: either just for you or for everyone. Here they have one more: upvalues, where the variable is local to a parent, so children environment can access them but the parent’s parents cannot. They are strange beasts as well, e.g. the code itself cannot really know if a variable is upvalue or global, only that it can access that.

And of course these scopes help embedding to not just be possible but straightforward and powerful. Local environments can be restricted, some things selectively enabled, and all this transparently, so the script running might not even know that it’s being in the Matrix.

The Lua Experience

Good

  • Fast, both start up and running
  • Language itself is quite small, possible to wrap one’s head around quite easily
  • Written in ANSI C, so basically on every architecture where one can run C, one can have Lua as well
  • Quite a few program has Lua interpreter or interface built in, see the list of these at Wikipedia
  • Tables are great and once one mastered them, are really Swiss Army Knives
  • Built in interpreter (though could use a little love like iPython)
  • The “…” syntax for variable number of arguments
  • Astrological naming convention – modules are rocks, the exercises I linked previously are missions, web framework is Kepler

Bad

  • There seem to be a lot of reserved names (e.g. in metatables) that would be pretty much impossible to figure out with a book (and/or an iPython-like helpful environment), though this is a problem probably only when starting out with Lua

Ugly

  • While some complex things can be solved, some simple things can require complex coding (e.g. in case of the tables when using “__index” and “__newindex“) and there are things that are not even possible. Or I just misunderstood some sections of the book.
  • Using a lot of syntactic sugar (especially in the object oriented section), that I feel need some more practice to pick up, as things can be done in multiple ways
  • The tables’ syntactic sugar covered way of handling string keys, convenient when things go well, mighty confusing at even the slightest problem
  • Too few projects using Lua, too few sources of information (this is not the language’s fault, though)

Project

Originally I wanted to do some useful programming in every language I learn during the Language of the Month series. I failed with Scala (lazy), and now failed with Lua too (underestimating the difficulty). I’m using VLC a lot and it has Lua scripting enabled, so I wanted to do a plugin that can be useful for me later as well. This didn’t work out very well, mainly because it feels the VLC Lua interface is not very well documented, one mostly have to find some examples that exist already and use them. I ended up wasting a lot of time and still don’t quite understand how to do certain things I would like for my code, and don’t even know if it’s possible to do or not. Will come back to it later, until that here are a few links that helped me to get started:

  • VLC Lua FAQ – detailed list of available API functions, but almost no context and examples
  • Lua extensions in the VLC git repo – one can pick up something by checking out those examples
  • Example: Streaming Radio Player Extension – someone who have gone further down this road than me and has a working extension. Very educational, especially to see how concise and straightforward it can be, because the VLC Lua API seems to be thought out well.

Again, hopefully pick this up later (I mean it).

Categories
Programming

Language of the Month: Lua

New month, new language. So far in this series:

I think I do want to amend the original rules set up for this Language of the Month series. At first I though I can write a new project in any language I learn. That is probably too ambitious. So new rules: every month write a new project in the given language OR contribute to an open-source project in that language. This should take away most of the stress and add some social aspect as well. :)

Lua

I’m intrigued by this language because of it’s niche: scripting language within other software. How one sets out to do something like this? What are the requirements for the language, in terms of design, syntax and so on?

Lua programming language logo
See, the moon!

First impressions

So far I was trying out some code snippets and example scripts. First thing to notice was that Lua is pretty darn quick to start. And pretty quick to run as well, though I haven’t used it for very heavy computation yet. E.g. the “get_all_factors” code at the Lua Crash Course (using a larger example number, 1029384756) is timed at ~7ms, wheres the same version on Python (the language that I probably know best and compare other languages to) runs ~10x slower. The snappiness of a scripting language is a surprisingly happy feeling. :)

Tables look very interesting, how the same thing can implement several data structures at once (it’s like Python’s dict, list and kinda-struct at the same time).

Quite intriguing that the Lua Virtual Machine is stack based, probably that’s the reason the language is so embeddable. A while back I was looking for a language with small resource (especially memory) requirements. I had a few suggestions (Dalvik, Forth) that were interesting, but maybe Lua is the one?

The “local” keyword (and the reasons for having it) seems to be a possible source of many harder to debug scenarios. Got to keep this in mind, again not being in Pythonland anymore.

Interesting how the “function” can be defined inline, so looks like there’s essentially no need for a special “lambda” keyword, at the expense of tying a few characters more…

The interpreter is quite well done (with it’s intelligent indentation probably even better then ipython, though would love to see more colours ^^)

As an exercise, here’s a version of FizzBuzz:

function fizzbuzz(num)
   --[[--
   The usual FizzBuzz from Jeff Atwood
   Doing it a bit roundabout to try some Lua language features
   --]]--
   local answer = ""

   if (num % 5) == 0 then
      answer = "Fizz"
   end
   if (num % 3) == 0 then
      answer = answer .. "Buzz"
   end

   if answer ~= "" then
      print(answer)
   else
      print(num)
   end
end

-- Run the thing
for num=1,100,1 do
   fizzbuzz(num)
end

Links

This section will be updated gradually as I find more information.

(Edit: added the second part of this experiment.)

Install

Tutorials

Books

Articles and info

Source of code

Projects using Lua