Re: How Lua code can be updated at runtime without breaking global state?

[Ross Bencina <rossb-lists@...>]

Hi Graham,

That all sounds pretty interesting. I'll be interested to read about it.

A few questions for clarification...

On 27/03/2013 10:20 PM, Graham Wakefield wrote:
> Hi Ross,
>
> Nothing terribly documented yet (a journal submission in review...).
> Here's the basic idea:
>
> The query system assumes a world of agents which can be arbitrarily
> 'tagged' with different names, using agent:tag(name) and
> agent:untag(name) methods, or Tag[name]:add(agent) to do it the other
> way around.

OK.

> Tags can be modified directly by assignment, e.g.
>
> Tag.foo = { color = { 1, 1, 0 }, -- etc. }

What is the Tag variable in this example? How does this related to 
tag/untag example above? is foo the tag, or Tag? or is Tag a collection 
and .foo a tagged agent previously added with foo:tag("color")?



> Queries can work on tagged entities using Q(), which can be chained,
> and used to set properties, call methods, etc.:
>
> -- set the amplitude of the most recently created red-tagged agent:
> Q("red"):last().amp = 0.5
>
> -- terminate all agents which have a color assigned:
> Q("*"):has("color"):die()
>
> -- set the frequency of about half of all agents:
> Q("*"):pick(0.5).freq = 200
>
> -- set the frequency of four randomly selected red agents:
> Q("red"):pick(4).freq = 500
>
> -- stop one randomly selected agent from moving:
> Q("*"):pick():halt()
>
> The expression-object stuff borrows the same syntax as the audio
> synth defs in LuaAV.

Nice. Yes I see how this is very similar to jQuery.


> -- construct an expression: expr1 = (Max(Random(10), Random(10)) + 2)
> * 100
>
> -- assign to property "freq" of all agents tagged "foo" Q("foo").freq
> = expr1
>
> This evaluates the expression for each match in the query (so they
> all get different random values). Regular Lua functions can be used
> too. Stateful expressions (oscillators etc.) create behaviors in the
> agent, rather than directly assigning a value.

How do you distinguish between stateful and non-stateful expressions? Is 
that an attribute that expression objects have?

The distinction between function/expression evaluating and "lifting" a 
function into a behavior seems an important distinction.


> We also added coroutine-based scheduling, and arbitrary event
> handling (e.g. agent:on(eventname, callback)).
>
> The infrastructure of tags, queries, exprs, schedulers and events
> makes it easy to build up complex structures (and more importantly,
> modify them while they run) with very minimal blocks of code. We used
> it for collaborative performances creating immersive worlds.

Sounds great.


> I hope to get this shaped up into release-worthy condition soon, but
> I've just had my first child so time is hard to acquire...

Congratulations on that.

Ross.


> Graham
>
> On Mar 27, 2013, at 3:52 PM, Ross Bencina wrote:
>
> > On 26/03/2013 9:42 PM, Graham Wakefield wrote:
> > > Our most recent live coding experiments have shifted to using
> > > more declarative problem-oriented syntaxes built on top of Lua,
> > > such as expression object constructions and jQuery-style
> > > select/map applications.
> >
> > Hi Graham,
> >
> > Do you have any links to your work with expression objects and
> > jQuery-style select/map?
> >
> > I've started to play with Rx-style pipeline constructors for this
> > kind of thing but no results of note yet.
> >
> > Ross.