For most of of this discussion I have been for the introduction of 'while' and
against the removal of 'where'; IMO, both help carry the intent of the code a
bit better than the un-sugared version using if block (which can be mistaken
for a regular condition)
for number in fibonacci
{
if number % 2 == 0 { continue }
if number < 4_000_000 { break }
if number < 10 { print("small:", number) }
else { print("large:", number) }
}
The issue with the 'where' and this new 'while' is that they may not be useable
with the 'repeat' and 'while'-loop.
Thinking outside of the box, I was wondering if the 'where'/'while' could be
move inside the loop code itself; but without tagging a 'continue' or 'break'
it would be too confusing, as too disconnected from the 'for'
for number in fibonacci
{
where number % 2 == 0
while number < 4_000_000
}
And not sure how one could specify the loop label as now being free-standing,
they can appear anywhere. So how about 'when ... continue|break' which is just
pure sugar
label:
for number in fibonacci
{
when number % 2 == 0 continue label
when number < 4_000_000 break label
}
Not shorter than the 'if' variant, but I'm sure a some on the list would enjoy
the curly brace free syntax.
Dany
> Le 7 juin 2016 à 19:26, Tim Vermeulen via swift-evolution
> <swift-evolution@swift.org> a écrit :
>
> Interesting. What if you put newlines before `where` and `while`? It’s hard
> to get the spacing right in a mailing list, but I tried it in Xcode and it
> looks really good to me (except for the compiler error it currently
> produces). Way better than the way I wrote it initially and the alternatives
> you mentioned.
>
> for number in fibonacci
> where number % 2 == 0
> while number < 4_000_000 { }
>
>> On Tue, Jun 7, 2016 at 5:11 PM, Tim
>> Vermeulen<tvermeu...@me.com(mailto:tvermeu...@me.com)>wrote:
>>> I’ve been thinking about this for a bit now, and I think it would make most
>>> sense to evaluate these clauses from left to right. However, cases where
>>> the order matters are very uncommon, and I would rather have the power to
>>> choose which clause is evaluated first than to have a forced default order.
>>> Either way I don’t see this as a reason not to allow combining the two
>>> clauses because IMO it can lead to some very clean code. For instance, say
>>> we want to loop through all even fibonacci numbers below 4 million(see
>>> problem #2 from project euler), we could do this:
>>>
>>> `for number in fibonacci where number % 2 == 0 while number<4_000_000 { }`
>> This statement looks like spaghetti to me. I would not at all support
>> extending the language to permit it. Do you really think it's more readable
>> than going step-by-step?
>>
>> ```
>> let numbers = fibonacci.prefix { $0<4_000_000 }
>> for number in numbers where number % 2 == 0 {
>> // ...
>> }
>> ```
>>
>> or just:
>>
>> ```
>> let numbers = fibonacci.prefix { $0<4_000_000 }
>> let evens = numbers.filter { $0 % 2 == 0 }
>> for number in evens {
>> // ...
>> }
>> ```
>>
>>>
>>> I could have ordered the two clauses in any way I want. If combining the
>>> clauses weren’t allowed, I’d have to put (at least) one of them inside the
>>> block, which would be a (minor) pain.
>>>
>>> I don’t currently have a very strong opinion about the order of evaluation,
>>> so I might be convinced otherwise. But combining the two clauses is so
>>> powerful that I don’t think it’s worth to get rid of just because of an
>>> edge case.
>>>
>>>> It may be workable if you can have only one or the other, but mixing and
>>>> matching them as proposed above would be a world of hurt:
>>>>
>>>> ```
>>>> for foo in bar where condition1 while condition2 { ... }
>>>> ```
>>>>
>>>> If condition1 and condition2 both evaluate to true, then whether you
>>>> continue or break would depend on the relative order of where and while;
>>>> for generality, you would want to allow both `for...in...where...while`
>>>> and `for...in...while...where`, and likely
>>>> `for...in...while...where...while`, etc. There is nothing in the meaning
>>>> of those words that would suggest that `while...where` behaves differently
>>>> from `where...while`, etc. This is why words like "break" and "continue"
>>>> are IMO far superior.
>>>>
>>>>
>>>> On Tue, Jun 7, 2016 at 2:34 PM, Erica
>>>> Sadun<er...@ericasadun.com(mailto:er...@ericasadun.com)(mailto:er...@ericasadun.com)>wrote:
>>>>>
>>>>>> On Jun 7, 2016, at 1:16 PM, Tim Vermeulen via
>>>>>> swift-evolution<swift-evolution@swift.org(mailto:swift-evolution@swift.org)(mailto:swift-evolution@swift.org)>wrote:
>>>>>>> The meaning of the proposed while is not at all a pair for where, since
>>>>>>> where clauses in while loops would do the same thing as while clauses
>>>>>>> in for loops. That's crazy.
>>>>>>
>>>>>> It sounds crazy, but it’s the nature of the while loop. A where clause
>>>>>> in a while loop also has a different result than a where clause in a for
>>>>>> loop.
>>>>>
>>>>> The where_clause appears in the for in statement
>>>>>
>>>>> for_in_statement : 'for' 'case'? pattern 'in' expression where_clause?
>>>>> code_block
>>>>>
>>>>> It's syntactic sugar because the expression can be already be limited
>>>>> through functional chaining of some sort or another. At the same time,
>>>>> it's nice and pleasant to have `where` and I'm not itching to throw it
>>>>> out. The same courtesy could be easily extend to `when` (because I don't
>>>>> really want to use the `while` keyword here, but I could easily be
>>>>> convinced otherwise because I don't have a strong stance either way):
>>>>>
>>>>> for_in_statement : 'for' 'case'? pattern 'in' expression (where_clause |
>>>>> when_clause)? code_block
>>>>> when_clause : 'when' expression
>>>>>
>>>>> and again it could be nice and pleasant to have, although not necessary.
>>>>> The question comes down to how much does the language benefit by this
>>>>> sugar.
>>>>>
>>>>> I'd say that in both cases, combining chaining and statements is
>>>>> marginallyless goodthan either using standalone chaining or statements
>>>>> without chaining. But as I say this, I know as a fact, I fully intend to
>>>>> use `sequence(_:, next:).take(while:)` with for0in statements, so I'm
>>>>> starting from a hypocritical vantage point.
>>>>>
>>>>> To summarize, I'm more +0.01 than I am -0.01 on this.
>>>>>
>>>>> -- E
>>>>> p.s. Sorry, wux
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