I guess the problem with examples is their analysis may not surface a particular use case. I agree at runtime this example may allow the interpreter to not over import. The original question about how an interpreter may be non-deterministic is whether the rules that determine whether the interpreter is lazy or eager have not been defined yet. The example was an attempt on my part to have the developer drive how aggressive the interpreter is in prefetching resources. To summarize, there should be some rules that make each vendors interpreter behave like the next one, and there should be a way for the developer to make the interpreter prefetch even if the interpreter sees no reason to do so.
On Jan 15, 2010, at 4:11 PM, Mike Samuel <[email protected]> wrote: 2010/1/15 Kam Kasravi <[email protected]>: comments below... ________________________________ From: Mike Samuel <[email protected]> To: Kam Kasravi <[email protected]> Cc: kkasravi <[email protected]>; es-discuss <[email protected]> Sent: Fri, January 15, 2010 1:45:52 PM Subject: Re: Module system strawpersons 2010/1/15 Kam Kasravi <[email protected]>: Ihab, Mike - Thanks for the comments. Yes, my examples confused definition with declaration, thanks for the corrections. I think I still have some unanswered questions which I'll try and clarify as: 1. I'm still not clear what the module identifier represents. Something like 'a/b/c' could be a URI or associated with a URI. Commonjs implicitly adds a '.js' which suggests this maps to a REST construct. I think it would be helpful to clarify the above literal, the module.id, any relation to javascript namespace and a mapping to server resources since there is such an overlap with package management. 2. If the eagerness of the interpreter is determined by its implementation we could have lots of indeterminism across interpreters. There should Which sources of indeterminism do you foresee? Is this indeterminism as apparent to a network observer or as apparent to code running in the same interpreter? [Kam] the network observer. A given interpreter may end up making lots of fetches or a few depending when it decided to resolve the import's. probably be another construct that defines when resources are fetched. I'm not sure if the interpreter shouldn't be influenced by the developer. Could you rephrase this last sentence, please? [Kam] as an example. lets say a module contains 3 adapters: one that uses jQuery, one that uses Ext and one that uses YUI. A eager interpreter may fetch all three when evaluating the module. Yet if the choice of what framework to use (jQuery, Ext or YUI) was determined by the developer/user early on, then the interpreter would fetch 2 frameworks without needing to. If the developer had a way to indicating to the interpreter that 2 of the frameworks weren't needed then the behavior of the interpreter would be predictable. If the module needs all 3, then it needs to fetch all 3. But if only one adapter is needed, then there is presumably some code somewhere which chooses which adapter. Let's call it the bootstrapper. Then the module relationship looks like: bootstrapper imports YUI-adapter YUI adapter imports YUI bootstrapper passes adapter to framework as a module parameter Since modules are first class, and are parameterizable, dependencies can be injected without requiring over-import. By not importing the adapters that are not needed, the other libraries are not imported. Brendan, do you recall es4 where the concept of a unit was introduced? There was also some discussion where management and security where implicitly mapped to the '.' between identifier parts. I cannot find that reference. Kam ________________________________ From: Mike Samuel <[email protected]> To: kkasravi <[email protected]> Cc: es-discuss <[email protected]> Sent: Fri, January 15, 2010 11:20:48 AM Subject: Re: Module system strawpersons 2010/1/15 kkasravi <[email protected]>: Hi Mike, Ihab: One factor that would influence eager or lazy fetching is where the import keyword may appear within the ecmascript grammar. The proposal suggests it could appear anywhere an identifier could appear. For example: I believe it cannot appear where a LeftHandSideExpression is expected because a function cannot be assigned to. So no replacing foo.bar = baz with (import ...) = baz 1) function find(name) { var name = foo.bar.Baz.find(name); // identifier 'foo.bar.Baz' ... } Replacing foo.bar with import would yield 2) function find(name) { var name = (import 'foo/bar').Baz.find(name); Provisioning is separate from importing. The above is looking up Baz on a function instance which normally would be the same as var name = Function.prototype.Baz.find(name) I think normal usage would look like var name = (import ...)(module, instance, parameters).Baz.find(name) ... } Replacing foo.bar.Baz with import would yield 3) function find(name) { var name = (import 'foo/bar/Baz').find(name); ... } I provided 2) and 3) because its not clear where a module definition begins. The presumption by naming convention is that foo.bar.Baz can be found within a relative resource named ./foo/bar.js on some server. This metadata needs to be somehow made available to the javascript runtime. So in some ways module's need package info. Let's assume the correct one is 2). Looking at 2), current javascript behavior is always lazy fetching because the above function find fetching can be eager, but evaluation happens whenever the ImportExpr is reached, possibly not at all. may not be called immediately or not at all. The javascript runtime would not complain about identifiers that are not immediately accessed or not accessed at all. Doing eager fetching means that we would need to fetch all imports prior to eval. Impacts are: 1. We fetch more than necessary and immediately. User perception is the new js runtime is much slower. Eager fetching can be done, or can be delayed, or multiple module definitions could be fetched in the same transaction. The degree of eagerness is up to the interpreter. 2. We forces all import expressions to be statically defined. Summary: If import can appear in place of an identifier, there is no choice but to do lazy fetching. Lazy fetching without CPS (continuation passing style) support means you could not do (import foo/bar').Baz.find(name); Kam On Jan 14, 2010, at 2:29 PM, Mike Samuel wrote: Ok, so let me try to make sure I understand the special form in strawman:modules_emaker_style, by defining a mini-strawman and knocking it down. Consider a special form (f, definer) = defineDelayedFunction(); where f is a function that will block on first call until definer has been called with an arguments array and a function body upon which point it will behave as if it were defined via new Function(...) with those arguments and function body. definer raises an Error on second and subsequent calls. defineDelayedFunction could be used with an async channel like XMLHttpRequest to define a module system, but all module definitions would happen at execute time, so it cannot be used to define a module system that resolves definitions prior to body evaluation. In modules_emaker_style, imports are statically determinable, so the set of dependencies is fully satisfied before the Program is evaluated, and this can be done recursively to make full use of sockets. A browser could optimistically find import definitions and start downloading before the full script body is loaded. defineDelayedFunction would impose lazy fetching, but modules_emaker_style allows eager fetching. 2010/1/14 <[email protected]>: Hi Mike, On Thu, Jan 14, 2010 at 1:29 PM, Mike Samuel <[email protected]> wrote: Are these proposals mutually exclusive or complementary. If (1) and (2) are exclusive, is there a place to collect use cases for a module-off? For my part, I think (1) and (2) are counterproposals, but there may exist a bunch of cross-pollination. For example, I will probably end up stealing Kris's "import with" syntax sometime. I don't see the word module anywhere in the packages proposal besides footnotes. What is the relationship between packages and modules. The packages proposal was written with module proposal (1) in mind, but is compatible in the broad sense with either. It does say in the beginning that it "... is intended to satisfy the Uniform location and retrieval goal of modules_emaker_style". There are more details under "Use in import" (where I just updated the syntax a little bit). 2. http://wiki.ecmascript.org/doku.php?id=strawman:modules_emaker_style Module proposal, by Ihab, focusing on EMaker-style invocation semantics. "First class objects. To the extent possible, module system components must be represented as first-class ECMAScript objects." Does object exclude primitives such as strings, or is the goal to exclude abstractions like LexicalScopes and References? The point is that module system components are made to appear, to the extent possible, as first-class objects rather than unmentionable "static" magic. E.g., contrast Java where, if Foo is a class, the expression "Foo" by itself is not an object; generic class parameters are not objects; etc. -- which makes higher-order programming somewhat harder. "import" is added to the reserved keyword list? It should be reserved now, and is for sure reserved according to this proposal. "return { getX: function() { return x; }, getY: function() { return y; }," indentation Fixed, tx. "In the module’s code, this is initialized to a new object that is instanceof the module function" Does this mean that access to a module instance conveys authority to create new module instances? Yes. Just like any other ES function where it's return value is instanceof that function. "An import expression evaluates immediately to a module function despite the fact that the specified module may have been fetched by asynchronous means (e.g., nonblocking network operations). This is done by taking advantage of the fact that import is a special form." Does this require "import" to be a special form instead of a desugaring? Or can the special form be boiled down to a function which when called, delays until another function is invoked, presumably with a valid FunctionExpr string as its sole argument? Would that require a continuation-passing transform of the code after the desugared "import"? If so, that may not be semantics preserving. Ihab -- Ihab A.B. Awad, Palo Alto, CA _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
