diff --git a/2018/ruby/day_19.rb b/2018/ruby/day_19.rb
new file mode 100644
index 0000000..63c8fc5
--- /dev/null
+++ b/2018/ruby/day_19.rb
@@ -0,0 +1,118 @@
+require "minitest"
+require "minitest/pride"
+
+OPCODES = {
+  addr: ->(a, b, c) { ->(registers) { registers[c] = registers[a] + registers[b] } },
+  addi: ->(a, b, c) { ->(registers) { registers[c] = registers[a] + b } },
+  mulr: ->(a, b, c) { ->(registers) { registers[c] = registers[a] * registers[b] } },
+  muli: ->(a, b, c) { ->(registers) { registers[c] = registers[a] * b } },
+  banr: ->(a, b, c) { ->(registers) { registers[c] = registers[a] & registers[b] } },
+  bani: ->(a, b, c) { ->(registers) { registers[c] = registers[a] & b } },
+  borr: ->(a, b, c) { ->(registers) { registers[c] = registers[a] | registers[b] } },
+  bori: ->(a, b, c) { ->(registers) { registers[c] = registers[a] | b } },
+  setr: ->(a, b, c) { ->(registers) { registers[c] = registers[a] } },
+  seti: ->(a, b, c) { ->(registers) { registers[c] = a } },
+  gtir: ->(a, b, c) { ->(registers) { registers[c] = (a > registers[b]) ? 1 : 0 } },
+  gtri: ->(a, b, c) { ->(registers) { registers[c] = (registers[a] > b) ? 1 : 0 } },
+  gtrr: ->(a, b, c) { ->(registers) { registers[c] = (registers[a] > registers[b]) ? 1 : 0 } },
+  eqir: ->(a, b, c) { ->(registers) { registers[c] = (a == registers[b]) ? 1 : 0 } },
+  eqri: ->(a, b, c) { ->(registers) { registers[c] = (registers[a] == b) ? 1 : 0 } },
+  eqrr: ->(a, b, c) { ->(registers) { registers[c] = (registers[a] == registers[b]) ? 1 : 0 } },
+}
+
+class TestOpcodes < Minitest::Test
+  def test_mulr
+    registers = [3, 2, 1, 1]
+
+    OPCODES[:mulr].call(2, 1, 2).call(registers)
+
+    assert_equal [3, 2, 2, 1], registers
+  end
+
+  def test_addi
+    registers = [3, 2, 1, 1]
+
+    OPCODES[:addi].call(2, 1, 2).call(registers)
+
+    assert_equal [3, 2, 2, 1], registers
+  end
+
+  def test_seti
+    registers = [3, 2, 1, 1]
+
+    OPCODES[:seti].call(2, 1, 2).call(registers)
+
+    assert_equal [3, 2, 2, 1], registers
+  end
+end
+
+Instruction = Struct.new(:opcode, :args)
+
+class Program
+  def self.parse(input)
+    lines = input.lines
+    ip = lines.shift[/^#ip (\d)+$/, 1].to_i
+    instructions = lines.map {|line|
+      opcode, *args = line.split
+      opcode = opcode.to_sym
+      args = args.map(&:to_i)
+      Instruction.new(opcode, args)
+    }
+    new(ip, instructions)
+  end
+
+  attr_reader :registers
+
+  def initialize(ip, instructions)
+    @ip, @instructions = ip, instructions
+    @registers = Array.new(6, 0)
+  end
+
+  def run
+    return enum_for(__method__) unless block_given?
+
+    while (0...@instructions.length).cover?(@registers[@ip])
+      instruction = @instructions.fetch(@registers[@ip])
+      OPCODES.fetch(instruction.opcode)[*instruction.args][@registers]
+      yield self
+      @registers[@ip] += 1
+    end
+  end
+end
+
+class TestProgram < Minitest::Test
+  def test_program
+    program = Program.parse(<<~PROGRAM)
+      #ip 0
+      seti 5 0 1
+      seti 6 0 2
+      addi 0 1 0
+      addr 1 2 3
+      setr 1 0 0
+      seti 8 0 4
+      seti 9 0 5
+    PROGRAM
+
+    run = program.run
+    loop do
+      run.next
+    end
+
+    assert_equal [7, 5, 6, 0, 0, 9], program.registers
+  end
+end
+
+def solve(input)
+  program = Program.parse(input)
+  run = program.run
+  loop do
+    run.next
+  end
+  program.registers[0]
+end
+
+if __FILE__ == $0
+  require "minitest/autorun" and exit if ENV["TEST"]
+
+  puts solve(ARGF.read)
+end