diff --git a/Gemfile b/Gemfile
index 896d28a..00c7933 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,2 +1,3 @@
 source "https://rubygems.org"
 gem "yard"
+gem "pry"
diff --git a/Gemfile.lock b/Gemfile.lock
index b3289ce..eb0675d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,12 +1,18 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    coderay (1.1.2)
+    method_source (0.9.0)
+    pry (0.11.3)
+      coderay (~> 1.1.0)
+      method_source (~> 0.9.0)
     yard (0.9.14)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
+  pry
   yard
 
 BUNDLED WITH
diff --git a/console b/console
new file mode 100755
index 0000000..fa64462
--- /dev/null
+++ b/console
@@ -0,0 +1,6 @@
+#!/usr/bin/env ruby
+require "pry"
+require_relative "lib/rcircuit.rb"
+a=Port.new(8)
+b=Port.new(8)
+Pry.start()
diff --git a/lib/rcircuit.rb b/lib/rcircuit.rb
index 4115996..6c47c09 100644
--- a/lib/rcircuit.rb
+++ b/lib/rcircuit.rb
@@ -5,3 +5,4 @@ require_relative "rcircuit/not.rb"
 require_relative "rcircuit/and.rb"
 require_relative "rcircuit/or.rb"
 require_relative "rcircuit/xor.rb"
+require_relative "rcircuit/adder.rb"
diff --git a/lib/rcircuit/adder.rb b/lib/rcircuit/adder.rb
new file mode 100644
index 0000000..0ab0fc8
--- /dev/null
+++ b/lib/rcircuit/adder.rb
@@ -0,0 +1,13 @@
+class Adder < Device
+  def initialize(width, init_args)
+    add_input("a", width)
+    add_input("b", width)
+    add_output("out", width)
+    init_assign(init_args)
+    @mask=(2**width)-1
+  end
+
+  def on_change(data_val)
+    out.setval((a.val+b.val)&@mask)
+  end
+end
diff --git a/lib/rcircuit/device.rb b/lib/rcircuit/device.rb
index bd0018c..5ef7826 100644
--- a/lib/rcircuit/device.rb
+++ b/lib/rcircuit/device.rb
@@ -5,7 +5,6 @@ class Device
   # @param width [Integer] Width of the port
   # @return [void]
   def add_input(name, width=1)
-    self.class.class_eval{attr_reader name.to_sym}
     port = Port.new(width)
     instance_variable_set("@#{name}", port)
     port.add_callback { |val| on_change(val) }
@@ -38,7 +37,7 @@ class Device
     hash.each do |name, port|
       #check if there is a defined method (port) that matches
       if self.respond_to?(name)
-        method(name).call(port)
+        instance_variable_get("@#{name}").connect(port)
       else
         raise ArgumentError, "No defined input '#{name}'"
       end