10.3 Pattern Matching

# Pattern Matching

When getting and setting information into the Time State, it's possible
to use more complex keys than basic symbols such as `:foo` and
`:bar`. You can also use URL style strings called paths such as
`"/foo/bar/baz"`. Once we start working with paths, we can then start
taking advantage of Sonic Pi's sophisticated pattern matching system to
`get` and `sync` with 'similar' rather than 'identical' paths. Let's
take a look.

## Match any path segment

Let's assume we want to wait for the next event that has three path segments:

```
sync "/*/*/*"
```

This will match any Time State event with exactly three path segments,
regardless of their names. For example:

* `cue "/foo/bar/baz"`
* `cue "/foo/baz/quux"`
* `cue "/eggs/beans/toast"`
* `cue "/moog/synths/rule"`

However, it will *not* match paths with fewer or more path segments. The
following will not match:

* `cue "/foo/bar"`
* `cue "/foo/baz/quux/quaax"`
* `cue "/eggs"`

Each `*` means *any content*. So we could match paths with just one segment with `/*` or paths with five segments with `/*/*/*/*/*`

## Matching partial segments

If we know what the segment is going to start or finish with, we can use
a `*` in addition to a partial segment name. For example:
`"/foo/b*/baz"` will match any path that has three segments, the first
of which is `foo`, the last `baz` and the middle segment can be anything
that starts with `b`. So, it would match:

* `cue "/foo/bar/baz"`
* `cue "/foo/baz/baz"`
* `cue "/foo/beans/baz"`

However, it wouldn't match the following:

* `cue "/foo/flibble/baz"`
* `cue "/foo/abaz/baz"`
* `cue "/foo/beans/baz/eggs"`

You can also place the `*` at the start of the segment to specify the
last characters of a segment: `"/foo/*zz/baz"` which will match any 3
segment `cue` or `set` where the first segment is `foo`, the last is
`baz` and the middle segment ends with `zz` such as `"cue
"/foo/whizz/baz"`.

## Matching Nested Path Segments

Sometimes you don't know how many path segments you want to match. In
these cases you can use the powerful double star: `**` such as
`"/foo/**/baz"` which will match:

* `cue "/foo/bar/baz"`
* `cue "/foo/bar/beans/baz"`
* `cue "/foo/baz"`
* `cue "/foo/a/b/c/d/e/f/baz"`

## Matching Single Letters

You can use the `?` character to match against a single char such as `"/?oo/bar/baz"` which will match:


* `cue "/foo/bar/baz"`
* `cue "/goo/bar/baz"`
* `cue "/too/bar/baz"`
* `cue "/woo/bar/baz"`

## Matching Multiple Words

If you know that a segment may be one of a select number of words, you
can use the `{` and `}` matchers to specify a list of choices such as
`"/foo/{bar,beans,eggs}/quux"` which will only match the following:

* `cue "/foo/bar/quux"`
* `cue "/foo/beans/quux"`
* `cue "/foo/eggs/quux"`

## Matching Multiple Letters

Finally, you can match against a selection of letters if you use the
`[` and `]` matchers to specify a list of choices such as
`"/foo/[abc]ux/baz"` which will match only:

* `cue "/foo/aux/baz"`
* `cue "/foo/bux/baz"`
* `cue "/foo/cux/baz"`


You can also use the `-` character to specify ranges of letters. For example `"/foo/[a-e]ux/baz"` which will match only:

* `cue "/foo/aux/baz"`
* `cue "/foo/bux/baz"`
* `cue "/foo/cux/baz"`
* `cue "/foo/dux/baz"`
* `cue "/foo/eux/baz"`

## Combining Matchers

When calling `sync` or `get` you are free to combine matchers in any
order you see fit to powerfully match any Time State event created by
`cue` or `set`. Let's look at a crazy example:

```
in_thread do
  sync "/?oo/[a-z]*/**/ba*/{quux,quaax}/"
  sample :loop_amen
end

sleep 1

cue "/foo/beans/a/b/c/d/e/bark/quux/"
```

## OSC Pattern Matching

For those curious, these matching rules are based on the Open Sound
Control pattern matching specification which is explained in detail
here: http://opensoundcontrol.org/spec-1_0