Michael Lucas-Smith illustrates programming with streams and a helpful "functional" protocol added by the ComputingStreams package from Cincom Smalltalk's public repository. Michael makes the case that more code should be based on streams instead of collections, and use a common protocol like ComputingStreams instead of custom, one-off methods that won't play well with others. Streams are a better abstraction than collections because they inherently "delay" and scale up to and including infinitely long streams.
Streams are interesting creatures, fundamental to programming if you've got them available. See Structure and Interpretation of Computer Programming: "Streams Are Delayed Lists" and Richard Waters' Series package for Common Lisp for more examples.
Also this Smalltalk package is similar to Avi Bryant's Relational Object Expressions. ROE uses objects using the standard Smalltalk collections protocol to delay "realizing" complete, in-memory collections, enabling the original collections to be enormous numbers of rows in tables on disk. In the case of ROE the objects are delaying the eventual composition and execution of SQL, including the conditional expressions that may have narrowed the size of the selection.