More helpful debugging info

dataflow.rb

@@ -53,7 +53,7 @@ def __unify__(value)
       LOCK.synchronize do
         __activate_trigger__ if @__trigger__
         if @__bound__
-          raise UnificationError if self != value
+          raise UnificationError, "#{@__value__.inspect} != #{value.inspect}" if self != value
         else
           @__value__ = value
           @__bound__ = true
@@ -73,7 +73,7 @@ def __activate_trigger__
     def method_missing(name, *args, &block)
       LOCK.synchronize do
         unless @__bound__
-          return '#<Dataflow::Variable unbound>' if name == :inspect
+          return "#<Dataflow::Variable:#{__id__} unbound>" if name == :inspect
           if @__trigger__
             __activate_trigger__
           else

spec/inspect_spec.rb

@@ -3,7 +3,7 @@
 describe "An unbound variable" do
   it "should be inspectable for debugging purposes" do
     local do |unbound|
-      unbound.inspect.should == "#<Dataflow::Variable unbound>"
+      unbound.inspect.should =~ /#<Dataflow::Variable:[0-9]+ unbound>/
     end
   end
 end