Herself’s Artificial Intelligence

I’ve been hearing more and more about Lua and today finally had enough free time to download, install and play with it a bit.

I downloaded the source filse and they compiled and installed painlessly on the Mac, just follow the directions in the INSTALL file. There is a folder full of test applications. Open up a terminal and type:> lua hello.lua at a command prompt to be sure you’ve gotten everything up and running.

It is an odd looking language. Hello World looks like this:

– the first program in every language

io.write(”Hello world, from “,_VERSION,”!\n”)

Bisection method for solving de looks like this:
– bisection method for solving non-linear equations

delta=1e-6 – tolerance

function bisect(f,a,b,fa,fb)
local c=(a+b)/2
io.write(n,” c=”,c,” a=”,a,” b=”,b,”\n”)
if c==a or c==b or math.abs(a-b)
n=n+1
local fc=f(c)
if fa*fc<0 then return bisect(f,a,c,fa,fc) else return bisect(f,c,b,fc,fb) end
end

– find root of f in the inverval [a,b]. needs f(a)*f(b)<0
function solve(f,a,b)
n=0
local z,e=bisect(f,a,b,f(a),f(b))
io.write(string.format(”after %d steps, root is %.17g with error %.1e, f=%.1e\n”,n,z,e,f(z)))
end

– our function
function f(x)
return x*x*x-x-1
end

– find zero in [1,2]
solve(f,1,2)

( * These and several other example programs are included in the Lua download. )

You can keep your programs in text format and run them as scripts ( lua program.lua ) or you can compile them using the luac compiler into binary form. ( luac -o hello hello.lua )

Lua is dynamically typed, it can call and use C functions, it has it’s own threads so you can run routines concurrently * these are not OS threads.

The key word list for Lua is surprisingly small ( and, break, do, else, elseif, end, false, for, function, if, in, local, nil, not, or, repeat, return, then, true, until, while ) and it is a case sensitive language. All else is defined in lua_functions of which there are all the things you’d expect.

I found projects including Apache modules so you can use Lua for webscripts, Palm versions so you can write Palm programs with Lua, and more than a few games. Lua is used in game scripting and interactive AI scripting.

See also:
Cognitive Code develops software personal assistant using Lua

More information:
Lua Reference manuals
O’Reilly article, ‘Introducing Lua’
Introduction to Lua Programming
GameDev, ‘An Introduction to Lua’