What is the advantage of knowing that a list is infinite?
There is plenty of overlap with the *functions* defined in Data.List, but the *data types* are really different. Conor emphasizes this point by tabulating the different structure Streams, Lists and CoLists carry. This distinction makes perfect sense if you distinguish between data and codata. Languages such as Coq have separate types for (inductive) lists and (coinductive) streams. See the Coq standard libraries for instance: http://coq.inria.fr/V8.1/stdlib/Coq.Lists.List.html http://coq.inria.fr/V8.1/stdlib/Coq.Lists.Streams.html I've encountered the need for streams, as opposed to lists, on several occassions. I know that Ross Paterson's arrow library defines a Data.Stream as well (used in Control.Arrows.Internal). I'm sure these aren't the only places where you really want to use streams instead of lists. As far as name clashes are concerned, Andres Loeh suggested Codata.Stream. I realize this requires the creation of a new category of libraries, but its the best suggestion I've heard so far. Wouter