[swift-evolution] repeat loop enhancement

[Tyler Cloutier]

Even better (shorter)

loop {
    // code
}

loop for x in 0..<5 {
    // code
}

loop for var i = 0 while someCondition(i) {
    // code
}

loop for var i = 0 {
    // code
} while someCondition(i) // The i variable would likely have to be considered in scope in the while expression

loop 5 {
    // code
}

loop for var i = 0 while i < 5 {
    // code
} always i += 1



> On Dec 9, 2015, at 1:29 PM, Tyler Cloutier via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 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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>>> 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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> 
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