1 files changed, 24 insertions, 18 deletions
diff --git a/lib/rake/invocation_chain.rb b/lib/rake/invocation_chain.rb
index 8a01ab4c29..dae9a35915 100644
--- a/lib/rake/invocation_chain.rb
+++ b/lib/rake/invocation_chain.rb
@@ -3,44 +3,50 @@ module Rake
   ####################################################################
   # InvocationChain tracks the chain of task invocations to detect
   # circular dependencies.
-  class InvocationChain
-    def initialize(value, tail)
-      @value = value
-      @tail = tail
-    end
+  class InvocationChain < LinkedList
 
-    def member?(obj)
-      @value == obj || @tail.member?(obj)
+    # Is the invocation already in the chain?
+    def member?(invocation)
+      head == invocation || tail.member?(invocation)
     end
 
-    def append(value)
-      if member?(value)
-        fail RuntimeError, "Circular dependency detected: #{to_s} => #{value}"
+    # Append an invocation to the chain of invocations. It is an error
+    # if the invocation already listed.
+    def append(invocation)
+      if member?(invocation)
+        fail RuntimeError, "Circular dependency detected: #{to_s} => #{invocation}"
       end
-      self.class.new(value, self)
+      conj(invocation)
     end
 
+    # Convert to string, ie: TOP => invocation => invocation
     def to_s
-      "#{prefix}#{@value}"
+      "#{prefix}#{head}"
     end
 
-    def self.append(value, chain)
-      chain.append(value)
+    # Class level append.
+    def self.append(invocation, chain)
+      chain.append(invocation)
     end
 
     private
 
     def prefix
-      "#{@tail.to_s} => "
+      "#{tail.to_s} => "
     end
 
-    class EmptyInvocationChain
+    # Null object for an empty chain.
+    class EmptyInvocationChain < LinkedList::EmptyLinkedList
+      @parent = InvocationChain
+
       def member?(obj)
         false
       end
-      def append(value)
-        InvocationChain.new(value, self)
+
+      def append(invocation)
+        conj(invocation)
       end
+
       def to_s
         "TOP"
       end