On Tue, May 10, 2016 at 5:56 PM, Tyler Cloutier <[email protected]> wrote:
> > On May 10, 2016, at 3:13 PM, Xiaodi Wu <[email protected]> wrote: > > On Tue, May 10, 2016 at 3:30 PM, Tyler Cloutier via swift-evolution < > [email protected]> 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. > > > >> 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 < >> [email protected]> 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 < >> [email protected]> 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 >> [email protected] >> https://lists.swift.org/mailman/listinfo/swift-evolution >> >> >> _______________________________________________ >> swift-evolution mailing list >> [email protected] >> https://lists.swift.org/mailman/listinfo/swift-evolution >> >> >> >> _______________________________________________ >> swift-evolution mailing list >> [email protected] >> https://lists.swift.org/mailman/listinfo/swift-evolution > > >
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