I think a clearer syntax here would be
for n in 1...2 { }
as it casts no shadow of doubt about how many times the loop will be executed.
> On 10 May 2016, at 9:27 pm, Tyler Cloutier via swift-evolution
> <swift-evolution@swift.org> wrote:
>
> What would repeat 1 { } mean then? Repeat N? Would it run N or N + 1 times?
>
> That sounds a massive source of bugs.
>
>
>> On May 10, 2016, at 5:25 PM, Xiaodi Wu <xiaodi...@gmail.com> wrote:
>>
>> FWIW, repeat once means do twice.
>> On Tue, May 10, 2016 at 19:16 Tyler Cloutier <cloutierty...@aol.com> wrote:
>>>> 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>
>>>> wrote:
>>>>>
>>>>>> On May 10, 2016, at 3:59 PM, Xiaodi Wu <xiaodi...@gmail.com> wrote:
>>>>>>
>>>>>>> On Tue, May 10, 2016 at 5:56 PM, Tyler Cloutier <cloutierty...@aol.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> On May 10, 2016, at 3:13 PM, Xiaodi Wu <xiaodi...@gmail.com> wrote:
>>>>>>>>
>>>>>>>>> On Tue, May 10, 2016 at 3:30 PM, Tyler Cloutier via swift-evolution
>>>>>>>>> <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> 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> 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
>>>>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
>>>>>>>>>> swift-evolution mailing list
>>>>>>>>>> swift-evolution@swift.org
>>>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> swift-evolution mailing list
>>>>>>>>> swift-evolution@swift.org
>>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution@swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
