title:: Understanding Streams, Patterns and Events - Part 2
summary:: Patterns Introduction
related:: Tutorials/Streams-Patterns-Events1, Tutorials/Streams-Patterns-Events3, Tutorials/Streams-Patterns-Events4, Tutorials/Streams-Patterns-Events5, Tutorials/Streams-Patterns-Events6, Tutorials/Streams-Patterns-Events7
categories:: Tutorials>Streams-Patterns-Events

section::Patterns

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 code::asStream:: message by creating a link::Classes/Stream::. Once again there is a default implementation in class link::Classes/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.

code::
(
a = 7.asStream;
a.postln;
a.next.postln;
)
::

section::Pattern and its subclasses

There is a class named link::Classes/Pattern:: that provides more functionality for the concept of a pattern.

A link::Classes/Pfunc:: is a Pattern that returns a link::Classes/FuncStream::. The same function arguments are supplied as are supplied to FuncStream.

code::
(
var a, b;
a = Pfunc.new({ #[1, 2, 3, 4].choose });
b = a.asStream;			// make a stream from the pattern
5.do({ b.next.postln; });	// print 5 values from the stream
)
::

A link::Classes/Prout:: is a Pattern that returns a link::Classes/Routine::. The same function argument is supplied as is supplied to Routine.

code::
(
var a, b, c;
a = Prout.new({
		3.do({ arg i; 3.rand.yield; })
	});
// make two streams from the pattern
b = a.asStream;
c = a.asStream;
4.do({ b.next.postln; });	// print 4 values from first stream
4.do({ c.next.postln; });	// print 4 values from second stream
)
::

A link::Classes/Pseries:: is a Pattern that generates an arithmetic series.

code::
(
var a, b;
a = Pseries.new(10, 3, 8);	// stream starts at 10, steps by 3 and has length 8
b = a.asStream;
9.do({ b.next.postln; });	// print 9 values from stream
)
::

link::Classes/Pgeom:: is a Pattern that generates a geometric series.

code::
(
var a, b;
a = Pgeom.new(10, 3, 8);	// stream starts at 10, steps by factor of 3 and has length 8
b = a.asStream;
9.do({ b.next.postln; });	// print 9 values from stream
)
::

section::Math operations on Patterns

Patterns also respond to math operators by returning patterns that respond to code::asStream:: with appropriately modified streams.

Applying a unary operator to a pattern

code::
(
var a, b, c;
a = Pseries.new(0,1,10);	// a is a pattern whose stream counts from 0 to 9
b = a.squared;			// pattern b is a square of the pattern a
c = b.asStream;
12.do({ c.next.postln; });
)
::

Using a binary operator on a pattern

code::
(
var a, b, c;
a = Pseries.new(0,1,10);	// a is a pattern whose stream counts from 0 to 9
b = a + 100;			// add a constant value to pattern a
c = b.asStream;
12.do({ c.next.postln; });
)
::

section::Filtering operations on patterns

Patterns also respond to the messages code::collect::, code::select::, and code::reject:: by returning a new link::Classes/Pattern::.

The code::collect:: message returns a Pattern whose link::Classes/Stream:: is modified by a function in the same way as the collect message sent to a Collection returns a modified Collection.

code::
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
// b is a pattern whose stream adds 100 to even values
b = a.collect({ arg item; if (item.even, { item + 100 },{ item }); });
c = b.asStream;
6.do({ c.next.postln; });
)
::

The code::select:: message creates a pattern whose stream passes only items that return true from a user supplied function.

code::
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
// b is a pattern whose stream only returns the odd values
b = a.select({ arg item; item.odd; });
c = b.asStream;
6.do({ c.next.postln; });
)
::

The code::reject:: message creates a pattern whose stream passes only items that return false from a user supplied function.

code::
(
var a, b, c;
// a is a pattern whose stream counts from 0 to 9
a = Pseries.new(0,1,10);
// b is a pattern whose stream that only returns the non-odd values
b = a.reject({ arg item; item.odd; });
c = b.asStream;
6.do({ c.next.postln; });
)
::

section::Making Music with Patterns

Here is a variation of the example given in part 1 that uses a link::Classes/Pattern:: to create two instances of the random melody stream.

code::
(
	s = Server.local;
	SynthDef(\help_SPE2, { arg i_out=0, sustain=1, freq;
		var out;
		out = RLPF.ar(
			LFSaw.ar( freq ),
			LFNoise1.kr(1, 36, 110).midicps,
			0.1
		) * EnvGen.kr( Env.perc, levelScale: 0.3,
			timeScale: sustain, doneAction: 2 );
		//out = [out, DelayN.ar(out, 0.04, 0.04) ];
		4.do({ out = AllpassN.ar(out, 0.05, [0.05.rand, 0.05.rand], 4) });
		Out.ar( i_out, out );
	}).send(s);
)
(
// streams as a sequence of pitches
	var pattern, streams, dur, durDiff;
	dur = 1/7;
	durDiff = 3;
	pattern = Prout.new({
		loop({
			if (0.5.coin, {
				#[ 24,31,36,43,48,55 ].do({ arg fifth; fifth.yield });
			});
			rrand(2,5).do({
				// varying arpeggio
				60.yield;
				#[63,65].choose.yield;
				67.yield;
				#[70,72,74].choose.yield;
			});
			// random high melody
			rrand(3,9).do({ #[74,75,77,79,81].choose.yield });
		});
	});
	streams = [
		(pattern - Pfunc.new({ #[12, 7, 7, 0].choose })).midicps.asStream,
		pattern.midicps.asStream
	];
	Routine({
		loop({
			Synth( \help_SPE2, [ \freq, streams.at(0).next, \sustain, dur * durDiff ] );
			durDiff.do({
				Synth( \help_SPE2, [ \freq, streams.at(1).next, \sustain, dur ] );
				dur.wait;
			});
		})
	}).play
)
::

To go to the next file:
link::Tutorials/Streams-Patterns-Events3::
