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

[Dave Abrahams]

on Thu May 05 2016, David Hart <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.

Nobody's proposing to rename reduce to sequence, FWIW.

> 
> * 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