create_subnode

# File lib/irb/slex.rb, line 119
      def create_subnode(chrs, preproc = nil, postproc = nil)
        if chrs.empty?
          if @postproc
            D_DETAIL.pp node
            SLex.fail ErrNodeAlreadyExists
          else
            D_DEBUG.puts "change abstract node to real node."
            @preproc = preproc
            @postproc = postproc
          end
          return self
        end
        
        ch = chrs.shift
        if node = @Tree[ch]
          if chrs.empty?
            if node.postproc
              DebugLogger.pp node
              DebugLogger.pp self
              DebugLogger.pp ch
              DebugLogger.pp chrs
              SLex.fail ErrNodeAlreadyExists
            else
              D_WARN.puts "change abstract node to real node"
              node.preproc = preproc
              node.postproc = postproc
            end
          else
            node.create_subnode(chrs, preproc, postproc)
          end
        else
          if chrs.empty?
            node = Node.new(preproc, postproc)
          else
            node = Node.new
            node.create_subnode(chrs, preproc, postproc)
          end
          @Tree[ch] = node
        end
        node
      end