Lua

LUA quick start-up guide

Lua is a simple, general-purpose scripting language

Lua provides the performance and security, while being

extremely small and efficient

We believe that most people who are new to Lua will pick up

the basics in minutes and feel comfortable within hours

What is LUA?

Variables and Simple Data Types

Lua has variables and simple types include nil, string,
number (integer, floating point), and Boolean values

local name = "Edgar"
local x = 1
local pi = 3.14159
local flag = false

Literal values

Typically, Lua strings are enclosed in single or
double quotes. They can also be enclosed in
double brackets (e.g. [[hello world]]), which allows
newlines in the string literal

Lua Boolean literals are true and false

Strings

Strings are an essential Lua data type

local s = "Text " .. "concatenation"
local n = #s -- the length of s in bytes

Assignment

Lua uses '=' as the assignment operator. In addition to
typical assignment, Lua also supports multiple assignment

x = 3
x, y = 3, 4

Operators

Lua uses <, <=, ==, >=, >, ~= as comparison operators on
numeric values. Lua uses and, or, and not as logical operators

Tables

Lua has only one structured data type, tables, which
are associative arrays. The literal constructor "{}" represents
a new empty table

Constructors can also create members

local T = {}
local T['x'] = 4

local T = { x = 1, y = 3.14 }

If the member name is not a proper identifier name, then it
must be quoted and wrapped in brackets

If no member names are given, then the constructor is
treated like an array, with the key values 1, 2, 3, ….
The following are equivalent

Tables can act like records. The following are equivalent

local T = { ["+"] = "plus", ["-"] = "minus" }

local T = { "first", "second" }
local T = { [1] = "first", [2] = "second" }

local T["x"] = 5
local T.x = 5

Functions and Function Calls

Lua has functions and function calls

Unlike many languages, Lua
supports multiple return values

function func(n)
if n == 1 then
return 1
end
return n * func(n - 1)
end

function f(x, y)
return x + y, x - y
end

local a, b = f(4, 2)

Control Statements

Lua has if-elseif-else-then, while-loop,
and repeat-loop statements

if a < 0 then
a = -a
end

if a < b then
c = "less"
elseif a == b then
c = "equal"
else
c = "greater"
end

while a > 10 do
f(a)
a = a - 1
end

repeat
a = f(a)
until a == 0

Lua also has a general for-loop with
numeric indices. The for-loop includes two
or three index values that represent the start,
end, and (optional) step values

Lua also includes a for-loop that iterates
over the values in a list. This is often used to
iterate over the key/value pairs in a table using
either pairs(T) or ipairs(T)

Lua includes a break-statement
that will exit an enclosing loop

for i = 1, 9, 2 do
f(i)
end

for k, v in pairs(T) do
-- iterate over all entries in T
fn(k, v)
end

for k, v in ipairs(T) do
-- iterate over all integer-keyed
-- entries in T
fn(k, v)
end

for k, v in pairs(T) do
if k == 0 then break end
end