Play With Lua!

Another short post. It’s because I’m working on something.

A lot of languages have a ternary operator, that lets you do this:

int x = foo ? 1 : 2;

It’s an easy way to pack a conditional on to one line, especially useful when giving things default values. Another way is if the if statement returns a value, like in Ruby:

x = if foo
        1
    else
        2
    end

Read the rest of this entry »

Short one this time:

print( string.char( 0xe2, 0x98, 0x83 ) )

If you have a console that supports UTF-8, you’ll see a barely recognizable glyph of a snowman. If you don’t, here’s what you’re missing.

(happens to be my second-favorite website of all time, behind this one)

The handiness of this for roguelike development is plain. There’s a good character list (with hex codes) here.

If you, like me, are writing a text-mode Roguelike game in Lua, you’ll probably be interested in the thing I just published: a small Lua library for coloring text output to the console.

It lets you do things like this:

print(color.bg.green .. color.fg.RED .. "This is bright red on green")

Couldn’t be simpler. Enjoy!

I’ve wanted to do a small case study of making an extension for a long time now. I’m writing a Roguelike game in Lua, so I had a need for one, and knocked it together last night: a C extension to provide Lua with a function to read one key from the keyboard.

Read the rest of this entry »

In a few hours, on the 18th of January, a lot of sites are going to “go dark” to protest SOPA, the latest in a series of draconian, badly-thought-out laws to regulate the internet and computing in general. This is probably old news to you, and I’m going to spare you another explanation of why this particular bill is so bad. Instead, I want to talk about in general, why programming knowledge is so strongly correlated with getting upset about things like this. It’s kind of a long story, and it starts in ancient Greece.

For what it’s worth, this site won’t go dark. I think it’s more important to leave it up so you can read this post.
Read the rest of this entry »

So you have made a program in Lua. You want to give it to people to run. You run into two problems right away: one, you don’t want to require people to install Lua to run your program, and two, you may not want them to have your source code (if it’s a commercial program). So, what to do?

If we were in a language like C, we could precompile our program into a binary and distribute that. So, since Lua can very closely integrate with C, can we do that with Lua? The answer turns out to be “yes”.
Read the rest of this entry »

I am spending the time making a presentation on ZeroMQ for the Lone Star Ruby Conference.

I thought of this today, and I thought it might make an interesting short post. One of the small annoyances of Lua is that it doesn’t have a lot of convenient support for arrays. You can implement arrays with tables, of course, but they’re still tables: they don’t have default metatables (so you can’t do things like join), they don’t pretty-print (so it’s a hassle to see what you have), and there’s still only one iterator (using ipairs with a for loop). You can do it but it’s not exactly convenient. So I started thinking about how exactly I’d add all that stuff.
Read the rest of this entry »

I’m not an expert on Lua. I’ve been using it for less than a year; most of the time before that I wrote Ruby, JavaScript, Scheme, etc. It’s not a terribly large language. I usually tell people that if they know JavaScript they can learn Lua in a weekend, and that’s true as far as the syntax goes. But, there are several Lua idioms that are either complicated or just not explained well, and one of those is modules. You can get a long way coding in Lua without ever using a module, but eventually you’ll want to know how they work.

I’m going to explain what modules are for, how to use them, and most importantly why they work that way, and I’m going to do that by implementing Lua’s module system myself. Let’s begin:
Read the rest of this entry »

This is an adaptation of a chapter from The New Turing Omnibus, a great little tour of a few dozen areas of CS. This is about a way to compress a bitmap, to store it without storing each individual pixel.

The technique is called a quadtree. We’re going to split a bitmap up into four equally-sized chunks, then compress and store those. The savings comes from the fact that we aren’t going to store equivalent chunks twice.
Read the rest of this entry »