Lua Academy · Lesson

Defining and Calling Functions

Syntax for function declaration, calling conventions, and local vs global functions.

Function Syntax

Functions in Lua are defined with the function keyword. The body is a block terminated by end. Functions can be global or local. You call a function by appending parentheses with arguments. If you omit arguments, missing parameters receive nil.

function sayHello(name)
  print("Hello, " .. (name or "World") .. "!")
end

sayHello("Lua")   -- Hello, Lua!
sayHello()        -- Hello, World!

local function add(a, b)
  return a + b
end
print(add(3, 4))  -- 7

Return Values

Functions return values with return. Unlike most languages, Lua functions can return multiple values. If you don't explicitly return, the function returns nothing (zero values). Excess return values are discarded when the call is not the last expression in a list.

local function minMax(t)
  local lo, hi = t[1], t[1]
  for i = 2, #t do
    if t[i] < lo then lo = t[i] end
    if t[i] > hi then hi = t[i] end
  end
  return lo, hi
end

local lo, hi = minMax({5,2,8,1,9})
print(lo, hi)  -- 1  9

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