Module system strawpersons

Kam Kasravi kamkasravi at yahoo.com
Mon Jan 18 14:24:49 PST 2010


Hi Mike

The former but not in the way you've described. Rather 

module A:
this.getB= function() {
  return new (import 'B')();
}

module B:
this.getA = function() {
  return new (import 'A')();
}

If modules eagerly resolve imports then the above circular dependency would be a problem.
If modules lazily resolve imports then the above circular dependency would be ok.
If catch-alls were used then proxy's would be used and the circular dependency would be ok.
Current js has many examples of circular dependencies which are resolved by lazy evaluation.


Kam




________________________________
From: Mike Samuel <mikesamuel at gmail.com>
To: Kam Kasravi <kamkasravi at yahoo.com>
Cc: Andy Chu <andy at chubot.org>; kkasravi <kkasravi at me.com>; Brendan Eich <brendan at mozilla.com>; es-discuss <es-discuss at mozilla.org>
Sent: Mon, January 18, 2010 1:50:15 PM
Subject: Re: Module system strawpersons

I don't quite understand what is meant by circular dependencies in this context.
Are you talking about the graph of imports, or the graph of module instances?

If the former, how is it a problem?

If the latter, how could it occur without explicit user intent : a
module explicitly passing itself to a dependency?

E.g. in the former
   // fib.js
   var self = (import "fib.js");
   if (n < 2) { return n; }
   return self({ n: n - 2 }) + self({ n : n - 1 });
a module imports itself, and recursively invokes separate instances
which is stupid but does not result in a module being observed in a
partially initialized state.

In the latter:
    // foo.js
    var otherModuleMaker = (import "bar.js")({ baz: this });
module foo is explicitly allowing otherModuleMaker to observe it in an
uninitialized state.

2010/1/18 Kam Kasravi <kamkasravi at yahoo.com>:
> Andy
>
> yes I was referring to the circular dependency issue.
> Catch-alls would be useful for this, though it would be nice if
> they were automated, eg returning a proxy until the module was used.
> Doing it manually by developer would be too difficult.
> I realize modules are intended to just satisfy a function body and
> can be initialized as objects or called as functions, but since they
> have strong container semantics I wonder if they should
> have more than just an 'id' especially if they provide a gateway
> to what else is in the directory as in commonjs.
>
> Kam
>
> ________________________________
> From: Andy Chu <andy at chubot.org>
> To: Kam Kasravi <kamkasravi at yahoo.com>
> Cc: Brendan Eich <brendan at mozilla.com>; kkasravi <kkasravi at me.com>;
> es-discuss <es-discuss at mozilla.org>
> Sent: Mon, January 18, 2010 12:40:35 PM
> Subject: Re: Module system strawpersons
>
> On Mon, Jan 18, 2010 at 10:29 AM, Kam Kasravi <kamkasravi at yahoo.com> wrote:
>> Yes, that looks right, I also remember a reference to the 'dot' notation
>> where namespace
>> access would be arbitrated implicitly by objects representing the '.' It
>> may
>> have been in
>> one of Lars Hansen papers on gradual typing. In any case there was some
>> good
>> discussion
>> on meta-level objects and controlling capabilities or access.
>>
>> Was there any discussion in the past about parameterized modules or
>> units where recursively nested modules/units were brought up? If two
>> modules
>> refer to each other
>> and all imports are resolved eagerly then I think this would be a problem
>> where use cases would
>> abound.
>
> What are you referring to here?  I think you are hinting at the
> problem of circular dependencies using "import" semantics like Python
> and CommonJS.  Right now if you have mutually recursive modules, you
> get partially initialized modules, because the "program counter" just
> follows every require().  The CommonJS spec specifically allows the
> partially initialized modules I think.
>
> Personally I try to break up circular dependencies, but this behavior
> is not very friendly, so I think it would be better if Harmony
> supported circular dependencies in a more "correct" way.  So this is
> an advantage of the "makers" style semantics (separating module
> definition and configuration).
>
> The Newspeak paper talks explicitly about this:
> http://scholar.google.com/scholar?hl=en&source=hp&q=objects%20as%20modules%20in%20newspeak&um=1&ie=UTF-8&sa=N&tab=ws
>
> If you are initializing modules in topological order, and there is a
> circular dependency between A and B, he says to just make a dummy
> proxy object for B to pass into A, initialize A, and then initialize
> B.
>
> That also reminds me that a good use case for catchalls is making
> module-like objects.  I haven't seen any discussions of the 2 together
> but it's definitely worth thinking about how they interact.
>
> Andy
>
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>
>
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