Programming Language for Old Timers


by David A. Moon
February 2006 .. September 2008

Comments and criticisms to dave underscore moon atsign alum dot mit dot edu.


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Stream Protocol

A stream is a stateful object that effectively combines a sequence and an iteration state for that sequence. Unlike iterating through a sequence, iterating through a stream changes the stream.

The following method requirements constitute the stream protocol:

defprotocol stream
  end?(x is stream, result: end? is boolean)
  next(x is stream, result: element)
  advance(x is stream)
Their behavior is very similar to the methods of the same names of the sequence protocol. There is no start-iteration method, as this happens automatically when a stream is created. The advance method does not return anything in particular.

There is a pseudo-constructor method stream that takes a sequence and returns a stream that iterates through that sequence.


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