def find( str )
      super lambda { raise Errno::ENOENT, str } do |dir|
        path = extensions.find do |ext|
          file = dir.join str + ext
          break file if file.exist?
        end
        break path if path
      end
    end
def find( str )
      super lambda { raise Errno::ENOENT, str } do |dir|
        path = extensions.find do |ext|
          file = dir.join str + ext
          break file if file.exist?
        end
        break path if path
      end
    end
Attempts to find the given file in this path set.
 Raises Errno::ENOENT if the file cannot be found.