function

A named group of statements.

Functions help with organizing and reusing code. For example, functions make it easy to express the idea "Draw an @ symbol.":

function drawChar()
  -- Style the text.
  textAlign(CENTER, CENTER)
  textSize(20)

  -- Draw a flower emoji.
  text('@', 50, 50)
end

The function header begins with the keyword function. The function's name, drawLetter, is followed by parentheses (). The code after the function's name and parenthesis, before the closing end, is called the function's body. The function's body runs when the function is called like so:

drawLetter()

Functions can accept inputs by adding parameters to their headers. Parameters are placeholders for values that will be provided when the function is called. For example, the drawLetter() function could include a parameter for the flower's size:

function drawLetter(size) 
  -- Style the text.
  textAlign(CENTER, CENTER)

  -- Use the size parameter.
  textSize(size)

  -- Draw a @ char .
  text('@', 50, 50)
end

Parameters are part of the function's declaration. Arguments are provided by the code that calls a function. When a function is called, arguments are assigned to parameters:

--The argument 20 is assigned to the parameter size.
drawLetter(20)

Functions can have multiple parameters separated by commas. Parameters can have any type. For example, the drawLetter() function could accept Number parameters for the flower's x- and y-coordinates along with its size:

function drawLetter(x, y, size) 
  -- Style the text.
  textAlign(CENTER, CENTER)

  -- Use the size parameter.
  textSize(size)

  -- Draw a flower emoji.
  -- Use the x and y parameters.
  text('@', x, y)
end

Functions can also produce outputs by adding a return statement:

function double(x) 
  local answer = 2 * x
  return answer
end

The expression following return can produce an output that's used elsewhere. For example, the output of the double() function can be assigned to a variable:

local six = double(3)
text("3 x 2 = "..six, 50, 50)

Examples

function example 1

function setup()
  size(100, 100)

  describe('A black @ on a gray background.')
end

function draw()
  background(200)

  -- Call the drawChar() function.
  drawChar()
end

-- Declare a function that draws the '@' char at the
-- center of the canvas.
function drawChar()
  -- Style the text.
  textAlign(CENTER, CENTER)
  textSize(20)

  -- Draw an @ symbol.
  fill("black")
  text('@', 50, 50)
end

function example 2

function setup()
  size(100, 100)

  describe('A @ character on a gray background.')
end

function draw()
  background(200)
  fill(0)

  -- Call the drawChar() function and pass values for
  -- its position and size.
  drawChar(50, 50, 20)
end

-- Declare a function that draws a @ character at the
-- center of the canvas.
function drawChar(x, y, size)
  -- Style the text.
  textAlign(CENTER, CENTER)

  -- Use the size parameter.
  textSize(size)

  -- Draw a @ symbol.
  -- Use the x and y parameters.
  text('@', x, y)
end

function example 3

function setup()
  size(100, 100)

  describe('The message "Hello, world!" written on a gray background.')
end

function draw()
  background(200)
  fill(0)

  -- Create a greeting.
  local greeting = createGreeting('world')

  -- Style the text.
  textAlign(CENTER, CENTER)
  textSize(16)

  -- Display the greeting.
  text(greeting, 50, 50)
end

-- Return a string with a personalized greeting.
function createGreeting(name)
  local message = "Hello, "..name.."!"
  return message
end

function

Examples

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