Scope

Your code can only access data if that data is within its scope.

Indenting

While not required, please indent your code to indicate a new scope. It'll make it easier to read for you and everyone else, and it'll make it easy to identify each unique scope. You'll see plenty of examples of this through the code examples here and everywhere else.

Blocks

A block of code creates a new scope. A new block exists in the space between something and its accompanying end.

That's between:

• The parentheses and end of a function
• The then and end of a conditional
• The do and end of a for or while loop
• The repeat and until of a repeat-until

local y = nil

if true then 
    --[[
        This `x` only exists until this block closes.
        When it stops existing, we say it "went out of 
        scope".
    ]]
    local x = 10

    --[[
        This is a new block within the other one, 
        so it can still access `x`.
    ]]

    local function func()
        -- 10
        print(x)
    end
end

--[[
    Both print `nil`, because they exist nested in 
    a different scope.
]]
print(x)
print(func)

Other Files

Each working file is its own block, unable to access anything local to any block of another file.

file1.lua

local x = 10

include("file2.lua")

-- nil
print(y)

file2.lua

local y = 20

-- nil
print(x)

Here, even though file2.lua is read and executed by the program running file1.lua, and you might think file2.lua's block is inside file1.lua, neither has access to each other's local variables.