[swift-evolution] [Proposal] Refining Identifier and Operator Symbology

[David Sweeris]

Sent from my iPhone

> On Oct 20, 2016, at 09:03, Jonathan S. Shapiro via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> On Thu, Oct 20, 2016 at 12:12 AM, Austin Zheng via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> Freeze the set of allowed emoji to whatever the current version of the Unicode spec defines...
> 
> UAX31 won't include emojis in either space, because there is no clear consensus about where they belong (identifiers or operators). Individual languages can certainly add them to one space or the other, but should take care not to cross-contaminate. So if we add them to operators, we need to exclude any that are already part of normal identifiers and vice versa. That sanity restriction is technically necessary, but it shouldn't be an inconvenience in practical terms.

My understanding (which is admittedly fuzzy) is that the distinction between operators and identifiers is only "technically necessary" because allowing characters to be both causes the parsing algorithm lose its virtual mind, and it takes a century for it to figure out what's going on. What I don't recall being discussed before is whether that's a blanket penalty or if the compile times increases are proportional to the amount overlap between the two character sets. If it's the latter, it might be worth discussing whether we should allow a *small* group of characters to be legal as both identifiers or operators, while maintaining sub-century compile times.

- Dave Sweeris.
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