diff --git a/2019/ruby/computer.rb b/2019/ruby/computer.rb
index 9c0e7ac..5842070 100644
--- a/2019/ruby/computer.rb
+++ b/2019/ruby/computer.rb
@@ -83,14 +83,14 @@ class Computer
     @rb = T.let(0, Integer)
   end
 
-  sig {params(input: AnyIO, output: AnyIO).returns(Memory)}
+  sig {params(input: T.untyped, output: AnyIO).returns(Memory)}
   def run(input=STDIN, output=STDOUT)
     each(input, output).inject(nil) {|_,i| i }
   end
 
   sig {
     params(
-      input: AnyIO,
+      input: T.untyped,
       output: AnyIO,
       blk: T.nilable(T.proc.params(m: Memory).returns(T.nilable(Integer)))
     ).returns(T::Enumerator[Memory])
diff --git a/2019/ruby/day_11.rb b/2019/ruby/day_11.rb
index 49cf6da..8deea09 100644
--- a/2019/ruby/day_11.rb
+++ b/2019/ruby/day_11.rb
@@ -1,3 +1,5 @@
+# typed: ignore
+
 require "stringio"
 
 require_relative "computer"
diff --git a/2019/ruby/day_12.rb b/2019/ruby/day_12.rb
index 76ef919..6c9f38a 100644
--- a/2019/ruby/day_12.rb
+++ b/2019/ruby/day_12.rb
@@ -1,3 +1,5 @@
+# typed: ignore
+
 require "matrix"
 require "prime"
 require "set"
diff --git a/2019/ruby/day_13.rb b/2019/ruby/day_13.rb
new file mode 100644
index 0000000..8a217d8
--- /dev/null
+++ b/2019/ruby/day_13.rb
@@ -0,0 +1,103 @@
+# typed: ignore
+
+require "stringio"
+
+require_relative "computer"
+
+class Game
+  def initialize
+    @output = Hash.new(0)
+    @min_x, @max_x, @min_y, @max_y = 0, 0, 0, 0
+  end
+
+  def []=(x, y, value)
+    @output[[x, y]] = value
+
+    @min_x = [@min_x, x].min
+    @max_x = [@max_x, x].max
+    @min_y = [@min_y, y].min
+    @max_y = [@max_y, y].max
+  end
+
+  def ball_pos
+    @output.key(4)
+  end
+
+  def paddle_pos
+    @output.key(3)
+  end
+
+  def score
+    @output[[-1, 0]]
+  end
+
+  def to_s
+    min_x = [0, @min_x].max
+
+    screen = (@min_y..@max_y).map {|y|
+      (min_x..@max_x).map {|x|
+        tile(@output[[x, y]])
+      }.join
+    }.join("\n")
+
+    score = @output[[-1, 0]] || 0
+
+    "#{screen}\n#{score}"
+  end
+
+  private
+
+  def tile(id)
+    case id
+    when 0 then " "
+    when 1 then ?█
+    when 2 then ?▒
+    when 3 then ?▄
+    when 4 then ?@
+    else fail "unexpected tile id: #{id}"
+    end
+  end
+end
+
+class FollowBall
+  def initialize(game)
+    @game = game
+    @last_ball = nil
+  end
+
+  def gets
+    ball, paddle = nil, nil
+    until [ball, paddle].none?(&:nil?) && ball != @last_ball
+      ball = @game.ball_pos
+      paddle = @game.paddle_pos
+    end
+    @last_ball = ball
+
+    # puts @game
+
+    # STDIN.gets
+    ball[0] <=> paddle[0]
+  end
+end
+
+game = Game.new
+follow_ball = FollowBall.new(game)
+output, output_writer = IO.pipe
+
+Thread.new do
+  loop do
+    x, y, tile_id = 3.times.map { output.gets.to_i }
+    game[x, y] = tile_id
+  end
+end
+
+Thread.new do
+  program = File.read("day_13.txt").split(?,).map(&:to_i)
+  program[0] = 2
+
+  Computer.new(program).run(follow_ball, output_writer)
+
+  sleep 1
+
+  puts game.score
+end.join