[swift-evolution] repeat loop enhancement

[Tyler Cloutier]

Sorry, something is up with my email address. 


Oooh and one more, the Infinite Loop:

repeat {

}


> On Dec 9, 2015, at 12:58 PM, Tyler Cloutier via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
> I’m still of the belief that all types of loops could be condensed down to a single type of loop, the repeat-for loop
> 
> Consider:
> 
> 
> The for-in loop:
> 
> repeat for x in 0..<5 {
>     // code
> }
> 
> The C style for loop and the while loop:
> 
> repeat for var i = 0 while someCondition(i) {
>     // code
> } 
> 
> 
> The repeat while:
> 
> repeat for var i = 0 {
>     // code
> } while someConditionEvaluatedAfterFirstLoop() // The i variable would likely have to be considered in scope in the while expression
> 
> 
> The currently discussed repeat loop
> 
> repeat 5 {
>     // code
> }
> 
> All follow a very basic pattern: The repeat keyword followed by a for declaration of loop scoped variables, then either a condition in the case of while or an iterator in the case of for-in. Optionally the language could include an “always” keyword that would specify a set of statements that were guaranteed to execute after each run of the loop. For example:
> 
> repeat for var i = 0 while i < 5 {
>     
> } always i += 1
> 
> If this were the case then all current loop constructs and their features could be subsumed by a single type of loop (including the to-be-removed C style for). This does have the problem of increasing the length of some current loop constructs though, specifically for-in.
> 
> Tyler
> 
> 
> 
> 
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> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
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>> On Dec 8, 2015, at 10:05 PM, André Videla via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> How about having a default implementation in the standard library for it? 
>> We avoid syntactic sugar and we allow for this very simple yet useful expression.
>> And we’ve seen solutions in this thread using autoclosurses and extensions
>> 
>> 5.times {
>>    …
>> }
>> 
>> or a function
>> 
>> repeat(4) {
>>    …
>> }
>> 
>> all sound good to me.
>> 
>> - André
>> 
>> 
>> 
>> 
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>>> On 09 Dec 2015, at 06:58, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> On Dec 8, 2015, at 4:43 PM, Daniel Steinberg via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>> For me this comes up when teaching children or new programmers. (Perhaps not a valid use case)
>>> 
>>> 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
>>> 
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