Stacker

local nSize, bNew, nBase, stack, maxx, maxy = 8, true, 0, {}, term.getSize()

stack[ 0 ] = { math.floor( maxx/2 ) - 4, math.floor( maxx/2 ) + 4, bReverse = false }

local function gameOver()
	term.clear()
	local str = "Game Over!  Your Score: " .. #stack - 1
	term.setCursorPos( math.floor( (maxx - #str) / 2 ), maxy / 2 )
	print( str )
	term.setCursorPos( 1, 1 )
	error()
end

local function renderStack()
	if #stack - nBase > maxy / 2 then
		nBase = nBase + 1
	end
	term.setBackgroundColor( colors.white )
	for i = 0, #stack do
		if i + nBase > #stack then
			break
		end
		term.setCursorPos( stack[ i + nBase ][ 1 ], maxy - i )
		term.write( string.rep( " ", stack[ i + nBase ][2] - stack[ i + nBase ][1] ) )
	end
	term.setBackgroundColor( colors.black )
end

local function getInput()
	local new = bNew and { 1, nSize + 1, bReverse = false } or stack[ #stack ]
	local id = os.startTimer( 0.1 * (0.99^#stack) )
	while true do
		local event = { os.pullEvent() }
		if event[ 1 ] == "timer" and event[ 2 ] == id then
			if not new.bReverse then
				new[ 1 ] = new[ 1 ] + 1
				new[ 2 ] = new[ 2 ] + 1
				if new[ 2 ] > maxx then
					new.bReverse = true
				end
			else
				new[ 1 ] = new[ 1 ] - 1
				new[ 2 ] = new[ 2 ] - 1
				if new[ 1 ] <= 1 then
					new.bReverse = false
				end
			end
			if bNew then
				stack[ #stack + 1 ] = new
				bNew = false
			end
			break
		elseif event[ 1 ] == "key" and event[ 2 ] == keys.space then
			if new[ 1 ] < ( bNew and stack[ #stack ][ 1 ] or stack[ #stack - 1 ][ 1 ] ) then
				new[ 1 ] = ( bNew and stack[ #stack ][ 1 ] or stack[ #stack - 1 ][ 1 ] )
			end
			if new[ 2 ] > ( bNew and stack[ #stack ][ 2 ] or stack[ #stack - 1 ][ 2 ] ) then
				new[ 2 ] = ( bNew and stack[ #stack ][ 2 ] or stack[ #stack - 1 ][ 2 ] )
			end
			if new[ 2 ] - new[ 1 ] <= 0 then
				gameOver()
			end
			nSize = new[ 2 ] - new[ 1 ]
			if bNew then
				stack[ #stack + 1 ] = new
			else
				stack[ #stack ] = new
				bNew = true
			end
			break
		end
	end
end

while true do
	term.clear()
	renderStack()
	getInput()
end