Functions

lua function arguments

When a function is called, it can contain a comma-separated list of values between parenthesis, these are arguments. They are assigned to parameters based on the order in the function declaration.

function printNumbers(x, y)
  print("Your first number is: " .. x)
  print("Your second number is: " .. y)
end

-- 3 and 25 are our arguments
printNumbers(3, 25) 
-- Prints: 
-- Your first number is 3 
-- Your second number is 25

lua function declarations

Functions are declared using their name, which can be used to call the function later. Function declarations are built from:

The function keyword
The function’s name
An optional list of comma-separated parameters, enclosed by ()
The end keyword as the last line of the function

function printFavoriteColor(color) 
  print("Your favorite color is " .. color)
end

Functions

A function is a set of statements that are executed together when called using the function’s name.

function getTallestMountain()
  print("The tallest mountain is Mount Everest")
end

lua function return

A function can return, or pass back, values using the return keyword. Return ends function execution and returns the specified value to where the function was called.

function double(x)
  return 2 * x
end

doubledX = double(2)
print(doubledX) -- Prints: 4

lua function documentation

Lua’s built-in functions are all documented on Lua’s official website. For additional examples of these functions, the user-maintained documentation is also useful.

lua function parameters

When a function is declared it can contain parameters as inputs. These act as variables inside the function. These parameters are only assigned a value when the function is called.

function printNumber(number)
  print("Your number is: " .. number)
end

lua function calls

Functions can be called after they have been declared using the function’s name followed by parenthesis. When called, all the code inside the function’s declaration is run.

function printSquare(num)
   print(num * num)
end

printSquare(4) --Prints: 16
printSquare(2) --Prints: 4 
printSquare(16) --Prints: 256

lua functions nil parameters

If a function is called without passing in enough arguments, the nil value is assigned to the remaining parameters.

function printAge(age)
  print("You are " .. age .. " years old")
end

printAge() -- Prints: You are nil years old

lua function built-ins

Lua has several built-in functions. Most are automatically included and can be called with no additional code. Some built-in functions include the print() and type() functions.