Get started with Lua programming

Get started with
Lua programming
 
Etiene Dalcol
@etiene_d

@etiene_dTopConf Tallinn 2015
@etiene_d

Sailor!
An MVC web framework in Lua 
sailorproject.org

Lua Ladies 
A female Lua user group 
lualadies.org

Google Summer of Code
LabLua

What’s Lua
Why Lua
Key Concepts
Going further

• Script Language
• Duck-typed
• Multi-paradigm
• procedural, OO, functional
• Garbage collection
• Coroutines
• First-class functions
• Lexical scoping
• Proper tail calls
• MIT License
What is Lua?

Why Lua?
Powerful.

Why Lua?
Size
(docs included)
First-class functions 
+
Lexical scoping
+
Metatables
Native C API
276 Kb
Object Orientation
Ada, Fortran, Java,
Smalltalk, C#, Perl,
Ruby etc.
+

Simple.Powerful.
Why Lua?

_G
_VERSION
assert
collectgarbage
dofile
error
getmetatable
ipairs
load
loadfile
next
pairs
pcall
print
rawequal
rawget
rawlen
rawset
require
select
setmetatable
tonumber
tostring
type
xpcall
bit32.arshift
bit32.band
bit32.bnot
bit32.bor
bit32.btest
bit32.bxor
bit32.extract
bit32.lrotate
bit32.lshift
bit32.replace
bit32.rrotate
bit32.rshift
coroutine.create
coroutine.resume
coroutine.running
coroutine.status
coroutine.wrap
coroutine.yield
debug.debug
debug.getuservalue
debug.gethook
debug.getinfo
debug.getlocal
debug.getmetatable
debug.getregistry
debug.getupvalue
debug.setuservalue
debug.sethook
debug.setlocal
debug.setmetatable
debug.setupvalue
debug.traceback
debug.upvalueid
debug.upvaluejoin
io.close
io.flush
io.input
io.lines
io.open
io.output
io.popen
io.read
io.stderr
io.stdin
io.stdout
io.tmpfile
io.type
io.write
file:close
file:flush
file:lines
file:read
file:seek
file:setvbuf
file:write
math.abs
math.acos
math.asin
math.atan
math.atan2
math.ceil
math.cos
math.cosh
math.deg
math.exp
math.floor
math.fmod
math.frexp
math.huge
math.ldexp
math.log
math.max
math.min
math.modf
math.pi
math.pow
math.rad
math.random
math.randomseed
math.sin
math.sinh
math.sqrt
math.tan
math.tanh
os.clock
os.date
os.difftime
os.execute
os.exit
os.getenv
os.remove
os.rename
os.setlocale
os.time
os.tmpname
package
package.config
package.cpath
package.loaded
package.loadlib
package.path
package.preload
package.searchers
package.searchpath
string.byte
string.char
string.dump
string.find
string.format
string.gmatch
string.gsub
string.len
string.lower
string.match
string.rep
string.reverse
string.sub
string.upper
table.concat
table.insert
table.pack
table.remove
table.sort
table.unpack

TopConf Tallinn 2015 @etiene_d
"Since Lua itself is so
simple, it tends to
encourage you to solve
problems simply."
Ragnar Svensson - Lead Developer at King
(Lua Workshop Oct 15 2015)

Fast.Simple.Powerful.
Why Lua?

http://www.humbedooh.com/presentations/ACNA%20-%20mod_lua.odp Introducing mod_lua by Daniel Gruno

My Reasons
• It looks cool
(I heard you could make games with it)
Better

Better Reasons
• It looks cool
• It’s made in my home country
(In my university to be more precise)

• It looks cool
• It’s made in my home country
(In my university to be more precise)
• It’s easy to learn
Better Reasons

• The index starts at 1
• There’s no continue
• The non-equality operator is ~=
• null is nil
• Comments are - -
• Only nil and false are equivalent to false
• Functions can genuinely return multiple values
• Variables are global by default
• Pattern matching is not regular expression
• The concatenation operator is ..
What’s different

Quick idioms
• a, b = b, a
• There’s no ternary operator but you can  
return x==1 and “yes” or “no”
• The access to local variables is faster than global
local match = string.match

Using Lua: three approaches
Embedded Scripting General-purpose

Getting Lua
• lua.org > download
• OS package manager
• apt-get install lua
• brew install lua
LuaRocks
• luarocks.org > install
• OS package manager
• apt-get install luarocks

Key Concepts

 
• The only way to structure data
• Array, dictionary, object, list, queue, module…
• Any value can be a key, except nil and nan
• Behind the scenes: array or hash table
• Passed as reference
• The length operator: #
• pairs(t) x ipairs(t)
Tables

Tables
Header
key value
“x” 9.2
nil
value
100
200
300
nil

 
• The only way to structure data
• Array, dictionary, object, list, queue, module…
• Any value can be a key, except nil
• Behind the scenes: array or hash table
• Passed as reference
• The length operator: #
• pairs(t) x ipairs(t)
Tables

Tables
local a = { 1, 3, 5, 7, 9}
local sum = 0
for i=1,#a do
sum = sum + a[i]
end
print(sum) -- 25

local a = { 1, 3, 5, 7, 9}
local sum = 0
for i=1,#a do
sum = sum + a[i]
end
print(sum) -- 25
Tables
local a = {}
a[1] = 1
a[2] = 3 -- etc
local sum = 0
for _, x in ipairs(a) do
sum = sum + x
end
print(sum)

local a = { 1, 3, 5, 7, 9}
local sum = 0
for i=1,#a do
sum = sum + a[i]
end
print(sum) -- 25
local a, x = 10, “y”
local point = { x = a, y = 25}
print(point[“x”], point[“y”]) -- 10 25
print(point[x], point[y]) -- 25 nil
print(point.x, point.y) -- 10 25
Tables

local a = { 1, 3, 5, 7, 9}
local sum = 0
for i=1,#a do
sum = sum + a[i]
end
print(sum) -- 25
local a, x = 10, “y”
local point = { x = a, y = 25}
print(point[“x”], point[“y”]) -- 10 25
print(point[x], point[y]) -- 25 nil
print(point.x, point.y) -- 10 25
-- sets and multisets
local ips = { “5.101.112.0” = true, “213.35.128.0” = true }
local connections = { “5.101.112.0” = 5, “213.35.128.0” = 2 }
Tables

-- Cipher module
--[[ Based on algorithms/caesar_cipher.lua
by Roland Yonaba ]]
local cipher = {}
local function ascii_base(s)
return s:lower() == s and ('a'):byte() or ('A'):byte()
end
function cipher.caesar( str, key )
return str:gsub('%a', function(s)
local base = ascii_base(s)
return string.char(((s:byte() - base + key) % 26) + base)
end)
end
return cipher
Modules

-- Cipher module
by Roland Yonaba ]]
local cipher = {}
end
function cipher.caesar( str, key ) --cipher.caesar = function(str,key)
end)
end
return cipher
Modules
public

-- Cipher module
by Roland Yonaba ]]
local cipher = {}
end
end)
end
return cipher
Modules
private

-- Cipher module
by Roland Yonaba ]]
local cipher = {}
end
end)
end
return cipher
Modules
local cipher = require “cipher”
print(cipher.caesar(“test”,3) -- whvw

 
• Overload operators
• Override built-in functions such as tostring
• Treat missing fields or intercept new field creation
• Call table as a function
• Metamethods: 
__add, __sub, __mul, __div, __mod, __pow, __unm,
__concat, __len, __eq, __lt, __le, __index, __newindex,
__call, __tostring, __ipairs, __pairs, __gc
Metatables

local mt = {}
local function new(r, i)
return setmetatable({ real = r or 0, im = i or 0}, mt)
end
local function is_complex(v)
return getmetatable(v) == mt
end
local function add(c1, c2)
if not is_complex(c1) then
return new(c2.real + c1, c2.im)
elseif not is_complex(c2) then
end
return new(c1.real + c2.real, c1.im + c2.im)
end
local function tos(c)
return tostring(c.real) .. "+".. tostring(c.im) .. "i"
end
mt.__add = add
mt.__tostring = tos
Complex numbers

local mt = {}
local function new(r, i)
return setmetatable({ real = r or 0, im = i or 0}, mt)
end
local function is_complex(v)
return getmetatable(v) == mt
end
local function add(c1, c2)
if not is_complex(c1) then
elseif not is_complex(c2) then
end
return new(c1.real + c2.real, c1.im + c2.im)
end
local function tos(c)
return tostring(c.real) .. "+".. tostring(c.im) .. "i"
end
mt.__add = add
mt.__tostring = tos
>local c1 = new(2,3) 
>print( c1 + 5 ) 
7+3i
Complex numbers

local square = { x = 10, y = 20, side = 25 }
function square.move(obj, dx, dy)
obj.x = obj.x + dx
obj.y = obj.y + dy
end
function square:area()
return self.side ^ 2
end
print(square:area()) -- 625
Objects

local square = { x = 10, y = 20, side = 25 }
function square.move(obj, dx, dy)
obj.x = obj.x + dx
obj.y = obj.y + dy
end
function square:area()
end
print(square:area()) -- 625
local square2 = (x = 30, y = 5, side = 10}
print(square.area(square2)) -- 100
Objects

local Square = {}
function Square:new(x, y, side)
local o = { x = x, y = y, side = side}
setmetatable(o, self)
self.__index = self
return o
end
function Square:move(dx, dy)
self.x = self.x + dx
self.y = self.y + dy
end
function Square:area()
end
return Square
Object Orientation

local Square = {}
function Square:new(x, y, side)
local o = { x = x, y = y, side = side}
setmetatable(o, self)
self.__index = self
return o
end
function Square:move(dx, dy)
self.x = self.x + dx
self.y = self.y + dy
end
function Square:area()
end
return Square
local Square = require “square”
local s1 = Square:new(10,20,25)
local s2 = Square:new(30,5,10)
print(s1:area()) -- 625
print(s2:area()) -- 100
Object Orientation

Going further

• Books
• Programming in Lua: http://www.lua.org/pil/
• Lua Programming Gems: http://www.lua.org/gems/
• Tutorials
• Lua Style Guide:  
http://lua-users.org/wiki/LuaStyleGuide
• Lua Missions: https://github.com/kikito/lua_missions 
• Misc
• CodeCombat: https://codecombat.com
• Community
• Lua mail list: http://www.lua.org/lua-l.html
Resources

 
• Hardware
• eLua: http://www.eluaproject.net/
• nodemcu: http://nodemcu.com 
• Math and scientific computing
• SciLua http://www.scilua.org/
• Torch: http://torch.ch
• GSL Shell: http://www.nongnu.org/gsl-shell/
Cool tools in Lua

 
• Game development
• Love2D: https://love2d.org/
• Defold: http://www.defold.com/
• Cocos2d: http://www.cocos2d-x.org/
• Corona: https://coronalabs.com 
• Web development
• OpenResty http://openresty.org
• Lapis: http://leafo.net/lapis/
• Luvit: https://luvit.io/
• Sailor: http://sailorproject.org/
• Moonshine: http://moonshinejs.org/
Cool tools in Lua

• IDE
• ZeroBrane Studio: http://studio.zerobrane.com/ 
• Testing
• Busted: http://olivinelabs.com/busted/
• Package management
• LuaRocks http://luarocks.org 
• Misc
• Moonscript: http://moonscript.org/
• Awesome Lua: 
https://github.com/LewisJEllis/awesome-lua
Cool tools in Lua

Thank you!
etiene.net 
github.com/Etiene/
dalcol@etiene.net
@etiene_d

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