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

[Dave Abrahams]

on Fri May 06 2016, Matthew Johnson <swift-evolution at swift.org> wrote:

>> 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.

Personally, I'm not confident “unfold” would be considered to meet the
utility bar, even if we changed the name of “reduce,” FWIW.

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

Personally I think “accumulate” does that better than either name, but
it doesn't matter.  What matters, IMO, is what more people will be
familiar with.

>
>
>> 
>>> 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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-- 
Dave