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

[Matthew Johnson]

> On May 6, 2016, at 7:30 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
> on Fri May 06 2016, Cole Campbell <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). 
> 
> It's not, IMO.  “Reduce” was chosen deliberately over “fold” because we
> think it is more in “common currency” among programmers, in no small
> part to the notice that MapReduce has gotten.

I was guessing this was the rationale.  But if it’s not too late and “fold” solves the “unfold” naming problem maybe we that balances out the equation.  

Which name do you think best communicates the essence of the operation?  IMO “fold” does a much better job of this.


> 
>> 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> 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> wrote:
>> 
>>            On May 5, 2016, at 1:03 PM, Erica Sadun <erica at ericasadun.com>
>>            wrote:
>> 
>>            On May 4, 2016, at 5:50 PM, Chris Lattner via swift-evolution
>>            <swift-evolution at swift.org> wrote:
>> 
>>                Proposal link:
>>                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
>> 
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> 
> -- 
> Dave
> 
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