diff --git a/2019/day5/intcode.rb b/2019/day5/intcode.rb
index 9ee5aa8..881d772 100644
--- a/2019/day5/intcode.rb
+++ b/2019/day5/intcode.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'forwardable'
+
 module Intcode
   def self.read(filename)
     parse File.read(filename)
@@ -14,7 +16,24 @@ module Intcode
     Program.new parsed
   end
 
+  class Program
+    def initialize(mem)
+      @input = nil
+      @initial_state = mem
+    end
+
+    def run(&user_input)
+      mem = Memory.new(@initial_state.clone)
+      Executor.new(mem).run(&user_input)
+    end
+  end
+
   class Memory
+    extend Forwardable
+
+    def_delegator :@cells, :[]
+    def_delegator :@cells, :[]=
+
     def initialize(cells)
       @cells = cells
     end
@@ -28,107 +47,103 @@ module Intcode
       end
       output
     end
-
-    def [](addr)
-      @cells[addr]
-    end
-
-    def []=(addr, val)
-      @cells[addr] = val
-    end
   end
 
-  class Program
-    attr_accessor :mem
+  class DoneExecuting < StandardError; end
+
+  class Executor
     def initialize(mem)
-      @input = nil
-      @initial_state = mem
+      @mem = mem
+      @ip = 0
     end
 
     def run(&user_input)
-      @mem = Memory.new(@initial_state.clone)
-      ip = 0
       loop do
-        opcode = operation(mem[ip])
-        mode = modes(mem[ip])
-        case opcode
-        when 1
-          r1 = mem[ip + 1]
-          r2 = mem[ip + 2]
-          r3 = mem[ip + 3]
-          a = param(r1, mode[0])
-          b = param(r2, mode[1])
-          raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
+        tick(&user_input)
+      rescue DoneExecuting
+        # TODO: Stop using exceptions for control flow
+        return
+      end
+    end
 
-          mem[r3] = a + b
-          ip += 4
-        when 2
-          r1 = mem[ip + 1]
-          r2 = mem[ip + 2]
-          r3 = mem[ip + 3]
-          a = param(r1, mode[0])
-          b = param(r2, mode[1])
-          raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
+    def tick(&user_input)
+      opcode = operation(@mem[@ip])
+      mode = modes(@mem[@ip])
+      case opcode
+      when 1
+        r1, r2, r3 = @mem[@ip + 1, 3]
+        a = param(r1, mode[0])
+        b = param(r2, mode[1])
+        raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
 
-          mem[r3] = a * b
-          ip += 4
-        when 3
-          r1 = mem[ip + 1]
-          raise StandardError, "unexpected mode: #{mode[0]}" if mode[0] != 0
+        @mem[r3] = a + b
+        @ip += 4
+      when 2
+        r1 = @mem[@ip + 1]
+        r2 = @mem[@ip + 2]
+        r3 = @mem[@ip + 3]
+        a = param(r1, mode[0])
+        b = param(r2, mode[1])
+        raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
 
-          mem[r1] = user_input.nil? ? input : user_input.call
-          ip += 2
-        when 4
-          r1 = mem[ip + 1]
-          output = param(r1, mode[0])
-          puts "output: #{output}"
+        @mem[r3] = a * b
+        @ip += 4
+      when 3
+        r1 = @mem[@ip + 1]
+        raise StandardError, "unexpected mode: #{mode[0]}" if mode[0] != 0
 
-          ip += 2
-        when 5
-          r1 = mem[ip + 1]
-          r2 = mem[ip + 2]
-          a = param(r1, mode[0])
-          b = param(r2, mode[1])
-          if !a.zero?
-            ip = b
-          else
-            ip += 3
-          end
-        when 6
-          r1 = mem[ip + 1]
-          r2 = mem[ip + 2]
-          a = param(r1, mode[0])
-          b = param(r2, mode[1])
-          if a.zero?
-            ip = b
-          else
-            ip += 3
-          end
-        when 7
-          r1 = mem[ip + 1]
-          r2 = mem[ip + 2]
-          r3 = mem[ip + 3]
-          a = param(r1, mode[0])
-          b = param(r2, mode[1])
-          raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
+        @mem[r1] = user_input.nil? ? input : user_input.call
+        @ip += 2
+      when 4
+        r1 = @mem[@ip + 1]
+        output = param(r1, mode[0])
+        puts "output: #{output}"
 
-          mem[r3] = a < b ? 1 : 0
-          ip += 4
-        when 8
-          r1 = mem[ip + 1]
-          r2 = mem[ip + 2]
-          r3 = mem[ip + 3]
-          a = param(r1, mode[0])
-          b = param(r2, mode[1])
-          raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
-
-          mem[r3] = a == b ? 1 : 0
-          ip += 4
-        when 99
-          return mem[0]
+        @ip += 2
+      when 5
+        r1 = @mem[@ip + 1]
+        r2 = @mem[@ip + 2]
+        a = param(r1, mode[0])
+        b = param(r2, mode[1])
+        if !a.zero?
+          @ip = b
         else
-          raise StandardError, "unexpected opcode: #{opcode}"
+          @ip += 3
         end
+      when 6
+        r1 = @mem[@ip + 1]
+        r2 = @mem[@ip + 2]
+        a = param(r1, mode[0])
+        b = param(r2, mode[1])
+        if a.zero?
+          @ip = b
+        else
+          @ip += 3
+        end
+      when 7
+        r1 = @mem[@ip + 1]
+        r2 = @mem[@ip + 2]
+        r3 = @mem[@ip + 3]
+        a = param(r1, mode[0])
+        b = param(r2, mode[1])
+        raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
+
+        @mem[r3] = a < b ? 1 : 0
+        @ip += 4
+      when 8
+        r1 = @mem[@ip + 1]
+        r2 = @mem[@ip + 2]
+        r3 = @mem[@ip + 3]
+        a = param(r1, mode[0])
+        b = param(r2, mode[1])
+        raise StandardError, "unexpected mode: #{mode[2]}" if mode[2] != 0
+
+        @mem[r3] = a == b ? 1 : 0
+        @ip += 4
+      when 99
+        raise DoneExecuting
+      else
+        raise StandardError, "unexpected opcode: #{opcode}"
       end
     end
 
@@ -162,12 +177,16 @@ module Intcode
     def param(val, mode)
       case mode
       when 0
-        mem[val]
+        @mem[val]
       when 1
         val
       else
         raise StandardError, "unexpected mode: #{mode}"
       end
     end
+
+    # Operators
+
+    def add; end
   end
 end