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

[Graham Wakefield <wakefield@...>]

On Mar 28, 2013, at 5:17 PM, Ross Bencina wrote:

> 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")?

Tag is the Lua module, foo is the tag name being modified. Changes to the tag like this will affect any new agents tagged with foo (or any existing agents that are re-tagged foo). So it's kind of like setting up a constructor preset. 

> 
> 
>> 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.

Yeah. It wouldn't be hard to extend this to more predicate types and more filters. The pick() filter in particular was widely used in performance. 

I should probably look at Haskell again for pattern-matching magic. 

>> -- 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?

Some expression primitives are stateful (e.g. SinOsc); and others inherit statefulness from their arguments. So Add(SinOsc(10), 3) is stateful.

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

More for the implementation than for the user, I think; in practice it's usually pretty obvious what will happen. We could have made the distinction more apparent in the syntax, but since 90% of the time it does what you'd expect, we opted for terseness. 

>> 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.

Hope to get some video of it soon.

> 
>> 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.

Thanks!


> 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.
>>> 
>> 
>> 
>> 
>