Often one wants to be able to create multiple streams from a single stream specification. Patterns are just a way to make multiple Streams from a single specification, like a cookie cutter. A pattern can be any object that responds to the
asStream message by creating a Stream. Once again there is a default implementation in class Object of asStream that simply returns the receiver as its own stream. Thus any object is by default a pattern that returns itself as a stream when sent the asStream message.
There is a class named Pattern that provides more functionality for the concept of a pattern.
A Pfunc is a Pattern that returns a FuncStream. The same function arguments are supplied as are supplied to FuncStream.
A Prout is a Pattern that returns a Routine. The same function argument is supplied as is supplied to Routine.
A Pseries is a Pattern that generates an arithmetic series.
Pgeom is a Pattern that generates a geometric series.
Patterns also respond to math operators by returning patterns that respond to
asStream with appropriately modified streams.
Applying a unary operator to a pattern
Using a binary operator on a pattern
Patterns also respond to the messages
reject by returning a new Pattern.
collect message returns a Pattern whose Stream is modified by a function in the same way as the collect message sent to a Collection returns a modified Collection.
select message creates a pattern whose stream passes only items that return true from a user supplied function.
reject message creates a pattern whose stream passes only items that return false from a user supplied function.
Here is a variation of the example given in part 1 that uses a Pattern to create two instances of the random melody stream.
To go to the next file: Understanding Streams, Patterns and Events - Part 3