Simple Scene Switching - Put the tabs in the following order: Main, Scene, BoxScene, CircleScene, Button

BoxScene.lua

BoxScene = class(Scene)

function BoxScene:init()
    -- We have to initialize our 
    --  super class
    Scene.init(self)
end

function BoxScene:draw()
    background(78, 99, 51, 255)
    
    fill(195, 154, 154, 255)
    rectMode(CENTER)
    rect(WIDTH/2,HEIGHT/2,300,300)
end

Button.lua

Button = class()

function Button:init(name, position, action)
    -- Name to appear on the button
    self.name = name    
    
    -- Location of the button (vec2 type)
    self.position = position
    
    -- Function to run when button is pressed
    self.action = action
    
    -- Default button size
    self.size = vec2(150,75)
end

function Button:draw()
    
    -- This lets us alter the style
    -- just for this button
    pushStyle()
    
    -- Tell Codea we want to draw from the center
    rectMode(CENTER)
    textMode(CENTER)
    
    -- Choose a font
    font("Inconsolata")
    fontSize(24)
    
    -- Pick a button color
    fill(153, 57, 57, 255)
    
    -- Draw a reddish rectangle at
    --  self.position with self.size
    rect( self.position.x, self.position.y, self.size.x, self.size.y )

    -- Use a white color for text
    fill(255)
    text( self.name, self.position.x, self.position.y )

    -- Old style is restored here
    popStyle()
end

function Button:containsPoint(x, y)
    -- Check if point x, y lies within the rectangle
    --  defined by self.position with self.size
    
    -- Get half the size for computing the bounds
    local halfSize = self.size * 0.5
    
    -- Figure out the lower left and upper right
    --  corners of our button
    local lowerLeft = self.position - halfSize
    local upperRight = self.position + halfSize
    
    -- Check if the point is inside them
    if x > lowerLeft.x and
       x < upperRight.x and
       y > lowerLeft.y and
       y < upperRight.y then
        -- Button contains point
        return true
    end
    
    -- Button does not contain point
    return false
end

function Button:touched(touch)
    -- Check three conditions necessary for a button tap:
    --  Touch has ended
    --  Touch is a "tap"
    --  The button actually contains the touch
    if touch.state == ENDED and 
       touch.tapCount == 1 then
        
        if self.action then
            -- If we have an action attached, run it
            self.action()
        end
        
    end
end

CircleScene.lua

CircleScene = class(Scene)

function CircleScene:init()
    -- We have to initialize our 
    --  super class
    Scene.init(self)    
end

function CircleScene:draw()
    background(51, 56, 99, 255)
    
    fill(154, 181, 195, 255)
    ellipse(WIDTH/2,HEIGHT/2,300,300)    
end

Main.lua

-- SimpleScenes

-- Use this function to perform your initial setup
function setup()
    -- Create two different scenes, these are subclasses
    --  of the Scene class
    boxScene = BoxScene()
    circleScene = CircleScene()
   
    -- Add a button to box scene to change to circle scene
    circleButton = Button("Circle Scene", 
                          vec2(WIDTH/2, 50), 
                          function() currentScene = circleScene end)
    boxScene:addButton(circleButton)
    
    -- Add a button to circle scene to change to box scene
    boxButton = Button("Box Scene", 
                          vec2(WIDTH/2, 50), 
                          function() currentScene = boxScene end)
    circleScene:addButton(boxButton)    
     
    -- currentScene represents the scene we are currently
    --  drawing. We can switch scenes by assigning a new value
    --  to this variable
    currentScene = boxScene
end

-- This function gets called once every frame
function draw()
    currentScene:drawScene()
end

function touched(touch)
    currentScene:touched(touch)
end

Scene.lua

Scene = class()

function Scene:init()
    self.buttons = {}
end

function Scene:addButton(button)
    self.buttons[button] = button
end

function Scene:removeButton(button)
    self.buttons[button] = nil
end

function Scene:drawScene()
    pushStyle()
    -- Draw our scene content
    self:draw()
    
    -- Now draw all our buttons
    for k,btn in pairs(self.buttons) do
        btn:draw()
    end
    
    popStyle()
end

function Scene:draw()
end

function Scene:touched(touch)
    -- Check if any buttons are touched
    for k,btn in pairs(self.buttons) do
        if btn:containsPoint(touch.x, touch.y) then
            btn:touched(touch)
            return
        end
    end
end