Lua Statements

[Leunsel]

In Lua, statements are the building blocks of control flow and logic. They define what your program does, how it executes, and when different blocks of code should run.

This guide covers Lua statements in depth, including expressions, control structures, declarations, and loops, with examples to help you understand each one clearly.

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What is a Statement?

A statement is a line or block of code that performs an action, such as assigning a value, looping, or calling a function.

Lua has simple statements (like assignment or function calls) and compound statements (like conditionals or loops).

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Expression and Assignment Statements

Assignment

x = 10
y, z = 1, 2

You can assign multiple values at once. Lua uses tuple unpacking.

Undefined variables are implicitly nil

print(unknown)  --> nil

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Looping Statements

1. while Loop

local i = 1
while i <= 5 do
  print(i)
  i = i + 1
end

2. repeat...until Loop

Runs the block at least once, then checks the condition.

local i = 1
repeat
  print(i)
  i = i + 1
until i > 5

3. for Numeric Loop

for i = 1, 5 do
  print(i)
end

-- with step
for i = 10, 1, -2 do
  print(i)
end

4. for Generic Loop

Used with iterators (e.g., pairs, ipairs):

local t = {a = 1, b = 2}
for k, v in pairs(t) do
  print(k, v)
end

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Conditional Statements

if, elseif, else

local score = 85

if score >= 90 then
  print("Grade: A")
elseif score >= 80 then
  print("Grade: B")
else
  print("Grade: C or below")
end

Lua treats false and nil as falsey; everything else is truthy (even 0 and empty strings).

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goto Statement

Lua supports labeled jumps (from 5.2+).

for i = 1, 5 do
  if i == 3 then goto skip end
  print(i)
  ::skip::
end

Use sparingly — it’s powerful but can make code hard to follow.

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return Statement

Used to return values from a function.

function add(a, b)
  return a + b
end

In top-level scripts (outside functions), return can terminate execution if needed.

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break Statement

Used to exit a loop early.

for i = 1, 10 do
  if i == 5 then break end
  print(i)
end

break is only valid inside loops.

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Block Statements

Blocks are sequences of statements grouped by do...end.

do
  local x = 42
  print(x)
end
-- x is not accessible here

Useful for creating limited scopes.

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Function Declarations (as Statements)

function greet(name)
  print("Hello, " .. name)
end

Or using anonymous function syntax:

greet = function(name)
  print("Hi, " .. name)
end

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Local Declarations

Local Variable

local count = 0

Local Function

local function hello()
  print("Hi")
end

Local declarations are scoped to the block they’re defined in.

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Full List of Lua Statement Types

Statement Type	Keyword(s)	Description
Assignment	=	Assigns values to variables
Function call	(implicit)	Invokes a function
if statement	if, elseif, else	Conditional branching
Looping	while, repeat, for	Executes code repeatedly
Block	do...end	Creates a scope
Return	return	Returns value(s) from a function
Break	break	Exits a loop early
Goto	goto, ::label::	Jumps to a labeled block
Local declaration	local	Declares local variables or functions
Function declaration	function	Defines a function

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Tips for Writing Clean Lua Statements

• Use local as much as possible to limit scope.
• Avoid deep nesting; use early return or break to simplify logic.
• Structure logic with clear blocks using do...end.
• Use for loops when iteration bounds are known; while when they are not.
• Limit use of goto to escape deeply nested logic when absolutely necessary.