Standardizing conditional try/catch

Alexander Jones alex at weej.com
Thu Mar 23 10:01:12 UTC 2017


To be clear I was talking about advanced pattern matching for exception
handling. Y(probably)AGNI?

On Tue, 21 Mar 2017 at 05:08, Isiah Meadows <isiahmeadows at gmail.com> wrote:

> It's possible to add a "[No LineTerminator here]" constraint when
> necessary, as was done for async functions.
>
> As for pattern matching, if you start paying attention to features of
> newer programming languages, especially those just getting past their
> hype stage (like Kotlin, Rust, and Swift), that YAGNI argument is
> starting to seem harder to accept.
>
> Pattern matching is to conditionals as async/await is to async tasks -
> it lifts the logic from fairly imperative, low level form to a high
> level, declarative form, with only a small loss of low-level control.
> -----
>
> Isiah Meadows
> me at isiahmeadows.com
>
>
> On Mon, Mar 20, 2017 at 8:42 PM, Alexander Jones <alex at weej.com> wrote:
> > Any future matching syntax would clearly support the special cases people
> > want to codify now. It might be that the best possible syntax is lost,
> but
> > e.g. ASI alone is probably a much bigger cause of syntax showstoppers to
> be
> > worried about. IMO, let it build up, then we can start thinking about a
> > syntax overhaul another day. The chances are that We Ain't Gonna Need It.
> >
> > On 19 March 2017 at 22:47, kdex <kdex at kdex.de> wrote:
> >>
> >> But then, we might be adding new syntax twice to solve the same problem.
> >> First specifically, then generally. The latter likely using an entirely
> >> different syntax, making the former syntax obsolete.
> >> Why not start speccing out some details for an optional typing proposal
> >> instead, so we can get the ball rolling for true pattern matching?
> >>
> >> On Sunday, March 19, 2017 11:18:25 PM CET Zach Lym wrote:
> >> > >
> >> > > I read that TC39 agreed on adding pattern matching to language in
> >> > > March
> >> > > 2013. 4 years later we don't have even stage 0 proposal - so I would
> >> > > consider it to be a dead end or wishful thinking.
> >> > >
> >> >
> >> > Exactly, this proposal has been kicking around for ~15 years but keeps
> >> > getting deferred in favor of "something better."  I would be all for a
> >> > special syntax using type hints or targeting easier-to-optimize
> subsets,
> >> > but they can be added later.
> >> >
> >> > This proposal introduces the minimum number of features needed to
> handle
> >> > the dynamic nature of JS.
> >> >
> >> > Thank you,
> >> > -Zach Lym
> >> >
> >> > On Sun, Mar 19, 2017 at 8:23 AM, kdex <kdex at kdex.de> wrote:
> >> >
> >> > > Well, there has been some discussion of potentially adding something
> >> > > like
> >> > > static type hints at some point in the future.
> >> > > Pattern matching is a feature that inevitably requires type
> >> > > information at
> >> > > runtime.
> >> > >
> >> > > So as long as the "optional typing" story isn't dead, I would assume
> >> > > that
> >> > > pattern matching isn't quite dead either, it's just not in the
> >> > > currently
> >> > > possible scope of things.
> >> > > ECMAScript wouldn't be the only language which would have taken
> years
> >> > > to
> >> > > come around to implementing type hinting: IIRC Python got its type
> >> > > hinting
> >> > > feature pretty late, too.
> >> > >
> >> > > On Sunday, March 19, 2017 4:22:26 PM CET Michał Wadas wrote:
> >> > > > Is there a serious push to add pattern matching to language? Does
> >> > > > any
> >> > > > popular dynamically typed language have pattern matching?
> >> > > > I read that TC39 agreed on adding pattern matching to language in
> >> > > > March
> >> > > > 2013. 4 years later we don't have even stage 0 proposal - so I
> would
> >> > > > consider it to be a dead end or wishful thinking.
> >> > > >
> >> > > > On Sat, Mar 18, 2017 at 5:16 PM, kdex <kdex at kdex.de> wrote:
> >> > > >
> >> > > > > I'm not sure if embedding this idea into the language will make
> >> > > > > future
> >> > > > > ideas about true pattern matching harder to implement or not.
> >> > > > > Destructuring assignments are pretty slow from what I've
> measured,
> >> > > > > and
> >> > > > > they still made it in, so I hardly see performance being a
> >> > > > > showstopper
> >> > > here.
> >> > > > >
> >> > > > > On Saturday, March 18, 2017 12:18:22 PM CET Michael J. Ryan
> wrote:
> >> > > > > > The if condition doesn't need to be limited to instance of...
> >> > > > > >
> >> > > > > > catch (err if !isNaN(err.status))
> >> > > > > >
> >> > > > > > Aside: entering code in a phone is hard...
> >> > > > > >
> >> > > > > > > `instanceof` doesn't work across realms (iframes, for
> >> > > > > > > example). If
> >> > > we
> >> > > > > > > introduced conditional catch blocks, I'd want a more
> reliable
> >> > > matching
> >> > > > > > > mechanism than instanceof.
> >> > > > > > >
> >> > > > > > > On Fri, Mar 17, 2017 at 5:01 PM, Zach Lym
> >> > > > > > > <zachlym at indolering.com>
> >> > > > > wrote:
> >> > > > > > >
> >> > > > > > >> Firefox supports the following conditional `catch` syntax:
> >> > > > > > >>
> >> > > > > > >>     try {
> >> > > > > > >>         let result = await ();
> >> > > > > > >>     } catch (e if e instanceof ErrorType) {
> >> > > > > > >>         ...
> >> > > > > > >>     }
> >> > > > > > >>
> >> > > > > > >>
> >> > > > > > >> This was originally implemented in Spidermonkey as part of
> an
> >> > > > > > >> ES
> >> > > > > proposal
> >> > > > > > >> around 2000, but it was rejected for unknown reasons [0]. A
> >> > > > > > >> 2012
> >> > > > > email to
> >> > > > > > >> this list suggesting standardization of the syntax was
> passed
> >> > > over in
> >> > > > > favor
> >> > > > > > >> of waiting for a generic pattern matching facility [0][1].
> >> > > > > > >> Later
> >> > > > > > >> discussion suggests that the pattern matching proposal
> would
> >> > > > > > >> have
> >> > > > > been very
> >> > > > > > >> slow [2]. A proposal for a Java-like type-based conditional
> >> > > > > > >> was
> >> > > > > proposed in
> >> > > > > > >> 2016, but was criticized for lacking generality [2].
> >> > > > > > >>
> >> > > > > > >> If the above summary is accurate, I would like to try to
> >> > > standardize
> >> > > > > the
> >> > > > > > >> vanilla syntax once again.  It's imperative, general, and
> >> > > > > > >> doesn't
> >> > > > > preclude
> >> > > > > > >> the use of any hypothetical pattern matching functionality.
> >> > > > > > >>
> >> > > > > > >> Javascript's control flow has improved dramatically in
> recent
> >> > > years:
> >> > > > > > >> promises got rid of callbacks, `async`/`await` clipped
> >> > > > > > >> promise
> >> > > > > chains, and
> >> > > > > > >> classes make it easy to create custom Error objects that
> >> > > > > > >> preserve
> >> > > > > > >> stacktraces.  Conditional catch is the last bit of syntax
> >> > > > > > >> needed
> >> > > to
> >> > > > > make JS
> >> > > > > > >> look like it was designed to handle asynchronous functions.
> >> > > > > > >>
> >> > > > > > >> Thoughts?
> >> > > > > > >>
> >> > > > > > >> -Zach Lym
> >> > > > > > >>
> >> > > > > > >> [0]: https://esdiscuss.org/topic/conditional-catch-clause#
> >> > > content-10
> >> > > > > > >> [1]: https://esdiscuss.org/topic/conditional-catch
> >> > > > > > >> [2]:
> >> > > > > > >>
> https://esdiscuss.org/topic/error-type-specific-try-catch-bl
> >> > > > > > >> ocks#content-14
> >> > > > > > >>
> >> > > > > > >> _______________________________________________
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> >> > > > > > >> es-discuss at mozilla.org
> >> > > > > > >> https://mail.mozilla.org/listinfo/es-discuss
> >> > > > > > >>
> >> > > > > > >>
> >> > > > > > >
> >> > > > > > > _______________________________________________
> >> > > > > > > es-discuss mailing list
> >> > > > > > > es-discuss at mozilla.org
> >> > > > > > > https://mail.mozilla.org/listinfo/es-discuss
> >> > > > > > >
> >> > > > > > >
> >> > > > > >
> >> > > > >
> >> > > > > _______________________________________________
> >> > > > > es-discuss mailing list
> >> > > > > es-discuss at mozilla.org
> >> > > > > https://mail.mozilla.org/listinfo/es-discuss
> >> > > > >
> >> > > > >
> >> > > >
> >> > >
> >> > > _______________________________________________
> >> > > es-discuss mailing list
> >> > > es-discuss at mozilla.org
> >> > > https://mail.mozilla.org/listinfo/es-discuss
> >> > >
> >> > >
> >>
> >> _______________________________________________
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> >>
> >
> >
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> >
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