[swift-evolution] Strings in Swift 4

Chris Eidhof chris at eidhof.nl
Tue Jan 24 02:05:34 CST 2017

I agree that being able to implement parsers in a nice way can be a huge
step forward in being really good at string processing.

There are a couple of possibilities that come to mind directly:

1. Build parsers right into the language (like Perl 6 grammars)
2. Provide a parser combinator language (e.g.
3. Rely on external tools like bison/yacc/etc.
4. Make it easy for people to write hand-written parsers (e.g. by providing
an NSScanner alternative).

Some obvious drawbacks of each approach:

1. Lots of work, probably hard to get right?
2. Only way to do this, afaik, is using lots of functional programming
which might scare people off. Also probably it's hard to get performance as
fast as 1.
3. No clear integrated way to do this
4. You still have to know how to write a parser.

I would think that 4. would be a good step forward, and 1/2 would
definitely benefit from this.

Also, I'd love to have this functionality on sequence/collection types,
rather than Strings. For example, it can be tremendously helpful to parse a
binary format using proper parsers. Or maybe you would want to use an
event-driven XML parser as "tokenizer" and parse that. Plenty of cool

On Tue, Jan 24, 2017 at 8:46 AM, Russ Bishop via swift-evolution <
swift-evolution at swift.org> wrote:

> On Jan 23, 2017, at 2:27 PM, Joe Groff via swift-evolution <
> swift-evolution at swift.org> wrote:
> On Jan 23, 2017, at 2:06 PM, Ben Cohen via swift-evolution <
> swift-evolution at swift.org> wrote:
> On Jan 23, 2017, at 7:49 AM, Joshua Alvarado <alvaradojoshua0 at gmail.com>
> wrote:
> Taken from NSHipster <http://nshipster.com/nsregularexpression/>:
>> Happily, on one thing we can all agree. In NSRegularExpression, Cocoa has
>> the most long-winded and byzantine regular expression interface you’re ever
>> likely to come across.
> There is no way to achieve the goal of being better at string processing
> than Perl without regular expressions being addressed. It just should not
> be ignored.
> We’re certainly not ignoring the importance of regexes. But if there’s a
> key takeaway from your experiences with NSRegularExpression, it’s that a
> good regex implementation matters, a lot. That’s why we don’t want to rush
> one in alongside the rest of the overhaul of String. Instead, we should
> take our time to make it really great, and building on a solid foundation
> of a good String API that’s already in place should help ensure that.
> I do think that there's some danger to focusing too narrowly on regular
> expressions as they appear in languages today. I think the industry has
> largely moved on to fully-structured formats that require proper parsing
> beyond what traditional regexes can handle. The decades of experience with
> Perl shows that making regexes too easy to use without an easy ramp up to
> more sophisticated string processing leads to people cutting corners trying
> to make regex-based designs kind-of work. The Perl 6 folks recognized this
> and developed their "regular expression" support into something that
> supported arbitrary grammars; I think we'd do well to start at that level
> by looking at what they've done.
> -Joe
> I fully agree. I think we could learn something from Perl 6 grammars. As
> PCREs are to languages without regex, Perl 6 grammars are to languages with
> PCREs.
> A lot of really crappy user interfaces and bad tools come down to
> half-assed parsers; maybe we can do better? (Another argument against
> rushing it).
> Russ
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> swift-evolution at swift.org
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Chris Eidhof
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