How do you do a lazy map?

[John M. Dlugosz]

Consider something like a 'map' call, only I want it to be lazy.  I know that a 
list can contain internally iterators that generate elements as needed or 
perhaps in the background.  But how do you create such a thing?  Something like:

   @lazy_list := parallel-map { get_info($_) } @filenames;
--John