Not so much. At least with views over most Enumerables, its quite possible in Ruby -- that's the whole reason that Enumerable::Lazy exists.

The existing File class doesn't quite support it because of the way its iterators are implemented (particularly, they are one way) but the class is easily extended to allow it, e.g.:

  class RewindFile < File
    def each
      rewind
      each_char {|x| yield x}
    end
  end
 

  a = RewindFile.new "myfile.txt"
  c = a.lazy.each
            .with_index
            .find_all {|x,_| x=="\n"}
            .map {|_,y| y}