[swift-evolution] [Accepted with modifications] SE-0045: Add scan, prefix(while:), drop(while:), and unfold to the stdlib

[Gmail]

I would also be happy with ‘fold’/‘unfold’. The term of art argument applies to fold in the same way it does for ‘reduce’.

Otherwise (if we stick with ‘reduce’) I find both ‘induce’ and ‘expand’ to be good names. I can also suggest ‘accumulate’.
In each of these cases I prefer the local consistency of a pair of functions, both being verbs, over the global consistency of a pair of functions, one being a verb and one a noun (for consistency with other functions in the standard library). As such, I like the name ‘iterate’.


Regarding the name ’sequence’: I find that it works well as a name for the two versions that was specified in Revision 3:

func unfold<T>(_ initialElement: T, applying: T -> T) -> UnfoldSequence<T>
func unfold<T, State>(_ initialState: State, applying: State -> (T, State)?) -> UnfoldSequence<T>

corresponding to `iterate` and the list `unfoldr` (also a specialization of `ana` (for anamorphism)):
 
iterate :: (a -> a) -> a -> [a]
unfoldr :: (b -> Maybe (a,b)) -> b -> [a] 

But would like to point out that by putting the return type in the name, it makes it less suitable as a potential general name for unfolding to other data structures (e.g trees).

 - David

> On 06 May 2016, at 09:12, Cole Campbell via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I don't know if it's considered too late at this point to rename 'reduce', but I'll add an enthusiastic +1 to renaming it to 'fold' and adding 'unfold'. 'Fold' is just as obvious a name as 'reduce', IMO (actually I even prefer it). I think changing it now with other source-breaking changes is better than moving forward with 'reduce' and a corresponding function with a confusing name. Fold/unfold would fit in beautifully with the prefix/suffix pairings already in the standard library.
> 
> Cole
> 
> On May 6, 2016, at 1:29 AM, David Hart via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> If we are discussing naming changes to reduce, here's my personal opinion:
>> 
>> * When I first encountered it, I understood exactly what it did because I knew that term of art. If it was named sequence, I would have been confused.
>> * If we are discussing name changes, I'd personally vote to change it to fold. It is the other term of art used for it, and it makes unfold work.
>> 
>> David
>> 
>> On 05 May 2016, at 22:39, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> 
>>>> On May 5, 2016, at 1:03 PM, Erica Sadun <erica at ericasadun.com <mailto:erica at ericasadun.com>> wrote:
>>>> 
>>>> On May 4, 2016, at 5:50 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> Proposal link: https://github.com/apple/swift-evolution/blob/master/proposals/0045-scan-takewhile-dropwhile.md <https://github.com/apple/swift-evolution/blob/master/proposals/0045-scan-takewhile-dropwhile.md>
>>>>> 
>>>>> Sequence.prefix(while:) & Sequence.drop(while:) - These are *accepted* as specified in revision 3 of the proposal.
>>>> 
>>>> I'm still a little sad we didn't go for `prefix`/`suffix` or `take`/`drop` pairs that linguistically matched.Nonetheless I'm gratified these are hopping into the language. That said, I'm going to put on my painters cap to consider selecting some exterior latex for the feature I was most looking forward to in this proposal:
>>>> 
>>>> Core team writes:
>>>>> unfold(_:applying:) - This addition is *rejected* by the core team as written, but deserves more discussion in the community, and potentially could be the subject of a future proposal.  The core team felt that the utility of this operation is high enough to be worth including in the standard library, but could not find an acceptable name for it.  “unfold” is problematic, despite its precedence in other language, because Swift calls the corresponding operation “reduce” and not “fold”.  No one could get excited about “unreduce”.   “iterate” was also considered, but a noun is more appropriate than an verb in this case.  Given the lack of a good name, the core team preferred to reject to let the community discuss it more.
>>>> 
>>>> A few thoughts:
>>>> 
>>>> * I'm not sure why a noun is more appropriate than a verb. Reduce isn't a noun, prefix isn't a noun, drop isn't a noun. 
>>> 
>>> I’m not a naming guru, but my understanding is that ‘reduce’ was picked because it was term of art (like map), which is what allowed the misuse of a verb.
>>> 
>>> One idea that came out of the core team discussion was something like:
>>> 
>>>    sequence(from: 0) { $0 += 42 }
>>> 
>>> Since it returns a sequence.
>>> 
>>> -Chris
>>> 
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160506/58079cbc/attachment.html>