On Mon, Nov 5, 2012 at 11:52 AM, Irakli Gozalishvili <[email protected]>wrote:
> Hi, > > I keep running into cases where I would like to know if function is pure. > Although my interpretation of pure is not quite right but I don't know any > better name. By pure in this context I would refer to functions that don't > access an out scope variables and don't > do any mutations of itself or it's properties no references to itself > could be an option too. My intended use case for such a feature is to > allow transfer (by which I meant just coping) of such functions across > workers / processes. For example in Mozilla add-on > we have a context-menu API > https://addons.mozilla.org/en-US/developers/docs/sdk/latest/packages/addon-kit/context-menu.html > which has limited declarative syntax for context definitions where > specific context item should appear. There is also programable API through > content-script files where one could write a predicate function that > is invoked in the page scope with a node reference on which event > has occurred. In most though pure function would have being enough but > there is no way for us to know weather given function refers to outer scope > variables. Same use cases arise with web workers and node processes too, it > would be great if we had something like Function.isPure(f). Also as far as > I know jits already capture this info for optimisation purposes maybe > it could be exposed ? Another alternative could be pure(function() { …. }) > that would throw compile error if > function followed is not pure. > Hi Irakli, because of < http://wiki.ecmascript.org/doku.php?id=harmony:function_to_string>, you can now code this yourself in JS, but only by writing a full JS parser and scope analyzer. Alternatively, you can use SES < http://code.google.com/p/google-caja/source/browse/trunk/src/com/google/caja/ses/>, which evaluates the function in a scope preventing it from accessing any non-whitelisted external variables, without needing to parse it, and therefore without needing to determine whether it actually does so. We use this ability to safely copy closed functions at http://wiki.ecmascript.org/doku.php?id=strawman:concurrency#vats (last paragraph) and starting at http://wiki.ecmascript.org/doku.php?id=strawman:concurrency#vat.evallater_as_async-pgas -- Cheers, --MarkM
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