Snake in Fun Basic

size = 8.0
(w,h) = (80.,60.)
GraphicsWindow.Width = size * w
GraphicsWindow.Height = size * h
directions = [(1,0),(0,1),(-1,0),(0,-1)]
function opposite(dir)
   return Math.Remainder(dir+2, 4)
end
function position(shape)
   return (Shapes.GetLeft(shape), Shapes.GetTop(shape))
end
function create_snake(x,y,dir)
    (dx,dy) = directions[opposite(dir)]
    for i = 0 to 3
        segment = Shapes.AddRectangle(size,size)
        Shapes.Move(segment, size*(x+dx*i), size*(y+dy*i))
        snake[i] = segment
    end
    return snake
end
sub add_segment(snake,dx,dy)
	segment = Shapes.AddRectangle(size,size)
    Shapes.Move(segment,x+size*dx,y+size*dy)
    for i = Array.GetItemCount(snake) to 1 step -1
		snake[i] = snake[i-1]
    end
    snake[0] = segment
end
function move(snake,dx,dy)
    length = Array.GetItemCount(snake)
    last = snake[length-1]
    first = snake[0]
    (x,y) = position(first)
    for i = length-1 to 1 step -1
        snake[i] = snake[i-1]
    end
    Shapes.Move(last, x+size*dx, y+size*dy)
    snake[0] = last
end
function self_harm(snake)
    (x,y) = position(snake[0])
	length = Array.GetItemCount(snake)
    for i = 1 to length - 1
        (x1,y1) = position(snake[i])
        if x = x1 and y = y1 then
            return true
        end
    end
    return false
end
function hit_wall(snake)
    (x,y) = position(snake[0])
    return x <= 0.0 or y <= 0.0 or x >= w*size or y >= h*size
end
dir = 0
function OnKeyDown
    select case GraphicsWindow.LastKey
        case "Right"
            dir = 0
        case "Down"
            dir = 1
        case "Left"
            dir = 2
        case "Up"
            dir = 3
	end
end
GraphicsWindow.KeyDown = OnKeyDown
GraphicsWindow.BackgroundColor = "black"
GraphicsWindow.BrushColor = "yellow"
GraphicsWindow.PenColor = "orange"
GraphicsWindow.FontSize = 32.0
start:
    prompt = Shapes.AddText("Click to Start")
    Shapes.Move(prompt, 100, 200)
    while Mouse.IsLeftButtonDown <> true
    end
    Shapes.Remove(prompt)
    snake = create_snake(30,30,dir)
    spawn_count = 10
    apple = Shapes.AddEllipse(size,size)
    Shapes.Move(apple, -size,-size)
    while (self_harm(snake) or hit_wall(snake)) <> true
        Program.Delay(300)
        (dx,dy) = directions[dir]
        move(snake,dx,dy)
        if spawn_count > 0 then
            spawn_count = spawn_count - 1
            if spawn_count = 0 then
                x = Math.GetRandomNumber(w-1.0)*size
                y = Math.GetRandomNumber(h-1.)*size
                Shapes.Move(apple, x, y)
            end
        else
            (x,y) = position(snake[0])
            (x1,y1) = position(apple)
            if x = x1 and y = y1 then
                add_segment(snake,dx,dy)
                Shapes.Move(apple, -size, -size)
                spawn_count = 10
            end
        end
    end
    go = Shapes.AddText("Game Over")
    Shapes.Move(go, 100, 200)
    Program.Delay(5000)
    Shapes.Remove(go)
    Shapes.Remove(apple)
    for i=0 to Array.GetItemCount(snake)
        Shapes.Remove(snake[i])
    end
goto start