Kenneth at 15:10, 17 May 2014

2014-05-17T15:10:18Z

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Script up your application with Lua!
: Ryan Erickson (@ryan_erickson)

"Come learn about Lua, the embeddable language that's used in everything from game scripting to Wikipedia, in mobile to web development.
In this presentation, I'll give a short introduction to Lua, how it can be used to extend a C/C++ application, to allow complex scripting without losing performance. I'll also show some interesting Lua language features.
Lastly, I'll give a live demonstration of the ease of embedding Lua into a C application."

Script up your application with Lua
* Ryan Erickson
* http://www.untestedhacks.com
* Works at Control4

Ryan's home automation - http://ericksonfamily.com/

The Programming Language Lua - http://www.lua.org/

Lua: getting started - http://www.lua.org/start.html

Installation:
yum install lua

curl -R -O http://www.lua.org/ftp/lua-5.2.3.tar.gz
tar zxf lua-5.2.3.tar.gz
cd lua-5.2.3
make linux test

History:
* lua.org
* created in 1993 at PUC-RIO
* Predecessors: DEL and Sol (merged to Lua)
* Lua is Portuguese for Moon, not an acronym (play on words from Sol)

Focus:
* Simplicity for non-programmer audience
* Portability
* Designed to be easily embedded, extended
* Clean ANSI C code
* Garbage Collected

Why:
* Size (tiny) < 100kb DLL/LIB
* Runs on mobile / embedded devices
* Performance - interpreted faster than Pyuthon, Ruby, Perl, PHP
** Need faster? LuaJIT
** LuaJIT is C++ / Java 6 territory (luajit.org)

Momentum:
* Used a lot in games
* Adobe Lightroom and Photoshop
* First interpreted lanugage allowed on iOS
* Angry Birds / World of Warcraft
* Control4 uses

Safety:
* Code runs in sandbox
* Embedder chooses which modules to expose
* Host application can provide APIs / primitives to Lua engine

Language:
* Dynamically typed
* Whitespace not significant
** spaces, linebreaks, tabs, what you like
* Semicolons not required, and discouraged
* single line comments
* variables are global by default, 'local' keyword

Types:
* number, string, boolean, nil, table, function, userdata
* numbers are double by default
* can represent floats and integers
* no i++, i+=2. use i =i +1

Strings:
* single/double quote
* backslash to escape
* string concatenation uses '..' (not +)

nil:
* empty value
* evaluates to false
* frees item for garbage collection

tables:
* lua's single data structure
* simultaneous array and hashmap
a = {"apple", "banana"}
b = {lua = "cool", java = "sucks"}
c = a
print(c[3], b.fred, b.["java"], a.grape)
# orange 3 sucks nul
* arrays in Lua are 1 based

Comments:
-- this is a comment
--[[ this is a multi
line comment ]]

Functions:
* first class objects
function add(a, b)
print(a + b)
end
multiply = function(a, b) print(a * b) end
plus = add
plus(3,5)

Control:
if ... then ... elseif ... else ... End
do
print("one")
end
for i = 1, 10 do print(i) end
for k, v in pairs({"}} ???

C Programmer Hangups:
* no curly braces - uses begin... end
* No +=, ++
* Not equals is "~="
* Not is "not"
* arrays start at 1
* #array is not always right (if empty items in the middle)

C interface API
* set of functions allow C to interact with Lua
* functions to read/write lua global variables
* functions to call lua functions
* functions to register c functions to call within lua
* stack based parameter passing

Book:
* "Programming in Lua" - http://lua.org/pil

Reference PDF:
* http://lua-users.org/wiki/LuaShortReference

Demo:
<pre>
-- comment
print("test" .. os.date())

function rirc(user, message)
local no_err, errmsg = pcall(parseIRC, user, message)
if (no_error == false) then SendIRC("ryan", errmsg) end
end

function parseIRC(user, message)
message = message:gsub("%s", "") -- trim white space
if (message == "|reload") then
if (user == "ryan") then
dofile("default.lua")
end
end
if (message == "|echo") then
SendIRC(user, "hello")
end
if (message:find("|giflet") ~= nil) then
local figstr = message:sub(8)
local sd = io.popen("figlet " .. figstr)
while(line) do
SendIRC(user, line)
end
sd:close()
end

end
</pre>

[[Category:Lua]]
[[Category:OpenWest 2014]]

OpenWest 2014/Lua - Revision history

Kenneth at 15:10, 17 May 2014