> On May 10, 2016, at 3:56 PM, Tyler Cloutier via swift-evolution > <swift-evolution@swift.org> wrote: > >> >> On May 10, 2016, at 3:13 PM, Xiaodi Wu <xiaodi...@gmail.com >> <mailto:xiaodi...@gmail.com>> wrote: >> >> On Tue, May 10, 2016 at 3:30 PM, Tyler Cloutier via swift-evolution >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >> I’d actually say that I’m strongly in favor of allowing just a repeat >> keyword, although I wouldn’t support making 'while true’. >> >> Firstly it reduces clutter >> >> Can you explain what clutter you see? Unless I misunderstand what you're >> referring to, reducing the 10 letters in `while true` to the six letters in >> `repeat` is hardly "reducing clutter." >> >> and makes it very clear that the the code is just supposed to repeat. >> >> I disagree here also. It is not very clear at all that the code is supposed >> to repeat indefinitely, not to any audience. >> >> First, it would not be clear to users who are experienced in Swift and aware >> of this proposal. Code is meant to be read, and allowing the omission of a >> trailing clause to produce two very different behaviors means that it is not >> clear what `repeat {` means until you encounter the closing brace and check >> for what follows. Moreover, what follows could be the keyword `while` on the >> following line, and in that case you cannot know whether the expression that >> follows `while` is the beginning of a new while loop until you encounter or >> don't encounter a new opening brace. By contrast, `while true {` cannot be >> anything other than the beginning of an infinite loop. You already know that >> fact after reading 12 letters. >> >> Second, it would not be clear to users migrating from another C-family >> language. `while true { }` is immediately understood by users of any other >> related language. >> >> Third, it would not be clear based on a knowledge of English. In common use, >> "repeat" does not mean repeat forever; it means to repeat once (i.e. do >> something twice). If I ask you to repeat something you just said, I should >> hope that you do not keep reciting it over and over until I tell you to stop. >> >> Secondly it’s a very simple way of introducing new programmers to loops. >> It’s IMHO more clear to a new programmer that repeat will just repeat >> indefinitely vs while true. >> >> I can speak to this a little bit, having introduced a new programmer to >> loops very recently and having done so in the past as well. I have not >> encountered anyone who has trouble with the *concept* of looping--i.e. the >> idea that the same code can be run over and over. >> >> Where things get tricky is the difficulty of mastering the syntax of the >> while loop and, more problematic, the syntax of the classic for;; loop. >> Introducing a simple way to make something repeat forever does not solve >> this learning hurdle, because students will continue to have to contend with >> these other types of loops in order to be productive in the language. A >> special syntax for repeating forever is especially unhelpful because it is >> just functional enough that a discouraged student may choose to avoid >> learning other types of loops and instead combine the infinite loop with if, >> continue, and break. > > I’d also like to point out Chris’ comments on the > > repeat X { > > } > > discussion. > > “ > This is a very valid use case. > > FWIW, “repeat N {}” was originally designed and scoped into the Swift 2 > implementation of the feature, but was cut due to schedule limitations. > There is precedent for this sort of feature in many teaching oriented > languages (e.g. Logo). > > I’d say that the pro’s and con’s of this are: > > + Makes a simple case very simple, particularly important in teaching. > + Even if you aren’t familiar with it, you can tell at first glance what the > behavior is. > - It is “just syntactic sugar”, which makes the language more complex. > - It is a very narrow feature that is useful in few practical situations. > > -Chris > “ >
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/001234.html > In this case, I would say it’s not making the language any more complex given > that repeat-while is a current construct. Admittedly it is a very narrow > feature, but it’s also a small one. > >> >> Lastly, this isn’t the first time this has been brought up on this list and >> there was previously discussion about the fact that when people see the >> repeat keyword that it should naturally repeat indefinitely unless a where >> clause is specified. >> >> I do believe that this is the first time this suggestion has been introduced >> to the list. I do not recall any previous discussion focused on infinite >> loops; they have been about repeating a finite number of times, using >> proposed syntax such as `repeat 3 times { }` or variations on that theme. >> >> I also think the concern that an accidental infinite loop is any greater >> than it is currently. >> >> Code gets refactored and edited. We're discussing on another thread changing >> the rules about dangling commas in parameter lists for that very reason. If >> you try to move a block of code with a repeat...while loop but accidentally >> leave behind the last line, this syntax will cause you grief. >> >> Tyler >> >> >> >>> On May 10, 2016, at 1:09 PM, Erica Sadun via swift-evolution >>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>> >>> I do not see sufficiently measurable benefits to this proposal to add it to >>> the language. >>> It's easy enough to roll your own `repeatForever` function with trailing >>> closure. >>> >>> I also want to thank you for bring it up on-list. Not every idea is right >>> for Swift but it's >>> always refreshing to see innovative thoughts added to the discussion. >>> Please do not be >>> discouraged by the generally negative feedback on this particular idea. >>> >>> -- Erica >>> >>>> On May 10, 2016, at 1:27 AM, Nicholas Maccharoli via swift-evolution >>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >>>> >>>> Swift Evolution Community, >>>> >>>> Currently writing an infinite loop in swift looks either something like >>>> this: >>>> >>>> while true { >>>> if ... { break } >>>> //... >>>> } >>>> >>>> Or this: >>>> >>>> repeat { >>>> if ... { break } >>>> //... >>>> } while true >>>> >>>> But I think it might be best to change the syntax / behaviour of `repeat` >>>> to loop >>>> indefinitely if no trailing while clause is present: >>>> >>>> repeat { >>>> if ... { break } >>>> //... >>>> } >>>> >>>> while still allowing a trailing `while` clause as in: >>>> >>>> repeat { >>>> foo += bar >>>> } while foo.count < limit >>>> >>>> I also want to propose that it should be a compile time error to use >>>> single `Bool` constants as while loop conditions, so no more `while true { >>>> ... }` it would become `repeat { ... }` >>>> >>>> I was thinking of drafting a short proposal if there was enough positive >>>> feedback. >>>> >>>> How does it sound? >>>> >>>> - Nick >>>> _______________________________________________ >>>> swift-evolution mailing list >>>> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>> https://lists.swift.org/mailman/listinfo/swift-evolution >>>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >>> >>> _______________________________________________ >>> swift-evolution mailing list >>> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>> https://lists.swift.org/mailman/listinfo/swift-evolution >>> <https://lists.swift.org/mailman/listinfo/swift-evolution> >> >> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org <mailto:swift-evolution@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-evolution >> <https://lists.swift.org/mailman/listinfo/swift-evolution> > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org <mailto:swift-evolution@swift.org> > https://lists.swift.org/mailman/listinfo/swift-evolution > <https://lists.swift.org/mailman/listinfo/swift-evolution>
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