Seems like you're asking for a check for if the function is a closure. If it maintains references to variables outside the scope of the function.
So would an `isClosure` function work for at least a little of what you want? On Dec 7, 2017 11:11, "Alex Vincent" <[email protected]> wrote: > OK, OK, clearly, pure functions are a fantasy in JavaScript. Once again, > a great idea and a lengthy essay of a post falls to a real-world > situation. Nuts. > > What if there's a middle ground? In the case I was originally talking > about, the developer calling on my membrane controls how the callback > function executes. I just want to ensure that, when the callback is passed > *controlled > and trusted* arguments (including possibly "this"), the function doesn't > refer to anything outside those arguments and local variables derived from > them. Is that reasonable to ask for? > > Call this check "is relatively pure", or "is locally pure", if you > desire. If the inputs themselves manipulate globals, "absolutely pure" can > never be guaranteed, as was just demonstrated... > > On Thu, Dec 7, 2017 at 9:35 AM, Michael Haufe <[email protected]> > wrote: > >> Relevant discussions: >> >> <https://groups.google.com/d/msg/mozilla.dev.tech.js-engine/ >> aSKg4LujHuM/2Y9ORBwCIQAJ> >> >> and: >> >> <https://mail.mozilla.org/pipermail/es-discuss/2012-November >> /thread.html#26657> >> >> >> On Thu, Dec 7, 2017 at 11:15 AM, Michał Wadas <[email protected]> >> wrote: >> >>> Only extremely small subset of functions can be proven to be pure. And I >>> suppose that these functions are already optimized by engines. >>> >>> eg. >>> notPure = (a,b) => a + b; // implicit conversion with side effects can >>> happen >>> notPure = (a) => a && a.b; // getter can be called >>> notPure = (foo, bar) => Reflect.has(foo, bar); // proxy trap can be >>> called. Someone could overwrite Reflect.has >>> >>> etc. >>> >>> It would be better idea to have builtin decorator *@pure* that allow >>> engine to remove or reorganize function calls (and valid implementation can >>> treat it as no-op). >>> >> > > > -- > "The first step in confirming there is a bug in someone else's work is > confirming there are no bugs in your own." > -- Alexander J. Vincent, June 30, 2001 > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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