more meaningful attribute accessors

Author: phluid61

trees/generic_list.rb

@@ -10,7 +10,7 @@ def initialize value, nxt=nil, prv=nil
       @prv = prv
     end
     attr_accessor :value
-    attr_accessor :nxt, :prv
+    attr_reader :nxt, :prv
 
     ##
     # Create a new node and insert it after this one.