> On May 10, 2016, at 4:07 PM, Xiaodi Wu <xiaodi...@gmail.com> wrote: > > > > On Tue, May 10, 2016 at 6:02 PM, Tyler Cloutier <cloutierty...@aol.com > <mailto:cloutierty...@aol.com>> wrote: > >> On May 10, 2016, at 3:59 PM, Xiaodi Wu <xiaodi...@gmail.com >> <mailto:xiaodi...@gmail.com>> wrote: >> >> On Tue, May 10, 2016 at 5:56 PM, Tyler Cloutier <cloutierty...@aol.com >> <mailto:cloutierty...@aol.com>> 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 >> “ >> >> 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. >> >> For the reasons I outlined above, I'd be +1 for `repeat N` and -1 for this >> case. >> > > That’s fair enough. :) > > But surely you’ll admit that if > > repeat N { > > } > > was valid, then repeat { } follows as the logical repeat indefinitely syntax, > no? > > No! Not at all! As I wrote above, it could mean repeat once. It currently > means repeat until the condition that follows, and if that condition is > optional you only find out after you read everything in the loop. So, IMO, it > does not follow at all! >
Let’s talk about this. Could it mean repeat once? No, it hasn’t been run yet. In fact, there is very clear syntax for exactly this: do { }. It means do this once. Currently, repeat-while means that you repeat while the condition is true. Thus if you leave off the condition it can only mean repeat this unconditionally. I really don’t think that this a huge logical leap, and I doubt very much that someone would be confused by it’s meaning. We will have to disagree here. I just see how adding a feature like repeat N, which increases complexity, would be better than extending the repeat syntax to allow you to repeat unconditionally. I’m +1 on this proposal (sans disallowing while true). Tyler > > >> >> >>> >>> 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>
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