lib/hamster/stack.rb in hamster-0.2.13 vs lib/hamster/stack.rb in hamster-0.3.0

@@ -1,7 +1,8 @@
 require 'forwardable'
 
+require 'hamster/immutable'
 require 'hamster/list'
 
 module Hamster
 
   def self.stack(*items)
@@ -10,12 +11,14 @@
 
   class Stack
 
     extend Forwardable
 
-    def initialize(list)
-      @list = list
+    include Immutable
+
+    def initialize
+      @list = EmptyList
     end
 
     def empty?
       @list.empty?
     end
@@ -28,20 +31,20 @@
     def top
       @list.head
     end
 
     def push(item)
-      self.class.new(@list.cons(item))
+      transform { @list = @list.cons(item) }
     end
     def_delegator :self, :push, :<<
 
     def pop
       list = @list.tail
       if list.empty?
         EmptyStack
       else
-        self.class.new(list)
+        transform { @list = list }
       end
     end
 
     def clear
       EmptyStack
@@ -52,15 +55,10 @@
       return false unless other.class.equal?(self.class)
       @list.eql?(other.instance_eval{@list})
     end
     def_delegator :self, :eql?, :==
 
-    def dup
-      self
-    end
-    def_delegator :self, :dup, :clone
-
     def to_a
       @list.to_a
     end
     def_delegator :self, :to_a, :entries
 
@@ -76,8 +74,8 @@
       @list.inspect
     end
 
   end
 
-  EmptyStack = Stack.new(EmptyList)
+  EmptyStack = Stack.new
 
 end