[swift-evolution] String update

[Eneko Alonso]

Could it be possible to specify the regex type ahead avoiding having to specify the type of each captured group?

let usPhoneNumber: Regex<UnicodeScalar, (area: Int?, routing: Int, local: Int)> = /
  (\d{3}?) -
  (\d{3}) -
  (\d{4}) /

“Verbose” alternative:

let usPhoneNumber: Regex<UnicodeScalar, (area: Int?, routing: Int, local: Int)> = / 
  .optional(.numberFromDigits(.exactly(3)) + "-“) +
  .numberFromDigits(.exactly(3)) + "-"
  .numberFromDigits(.exactly(4)) /
print(type(of: usPhoneNumber)) // => Regex<UnicodeScalar, (area: Int?, routing: Int, local: Int)>


Thanks,
Eneko


> On Jan 16, 2018, at 8:52 AM, George Leontiev via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Thanks, Michael. This is very interesting!
> 
> I wonder if it is worth considering (for lack of a better word) *verbose* regular expression for Swift.
> 
> For instance, your example:
> ```
> let usPhoneNumber = /
>   (let area: Int? <- \d{3}?) -
>   (let routing: Int <- \d{3}) -
>   (let local: Int <- \d{4}) /
> ```
> would become something like (strawman syntax):
> ```
> let usPhoneNumber = /let area: Int? <- .numberFromDigits(.exactly(3))/ + "-" +
>                     /let routing: Int <- .numberFromDigits(.exactly(3))/ + "-"
>                     /let local: Int <- .numberFromDigits(.exactly(4))/
> ```
> With this format, I also noticed that your code wouldn't match "555-5555", only "-555-5555", so maybe it would end up being something like:
> ```
> let usPhoneNumber = .optional(/let area: Int <- .numberFromDigits(.exactly(3))/ + "-") +
>                     /let routing: Int <- .numberFromDigits(.exactly(3))/ + "-"
>                     /let local: Int <- .numberFromDigits(.exactly(4))/
> ```
> Notice that `area` is initially a non-optional `Int`, but becomes optional when transformed by the `optional` directive.
> Other directives may be:
> ```
> let decimal = /let beforeDecimalPoint: Int <-- .numberFromDigits(.oneOrMore)/ +
>               .optional("." + /let afterDecimalPoint: Int <-- .numberFromDigits(.oneOrMore)/
> ```
> 
> In this world, the `/<--/` format will only be used for explicit binding, and the rest will be inferred from generic `+` operators.
> 
> 
> I also think it would be helpful if `Regex` was generic over all sequence types.
> Going back to the phone example, this would looks something like:
> ```
> let usPhoneNumber = .optional(/let area: Int <- .numberFromDigits(.exactly(3))/ + "-") +
>                     /let routing: Int <- .numberFromDigits(.exactly(3))/ + "-"
>                     /let local: Int <- .numberFromDigits(.exactly(4))/
> print(type(of: usPhoneNumber)) // => Regex<UnicodeScalar, (area: Int?, routing: Int, local: Int)>
> ```
> Note the addition of `UnicodeScalar` to the signature of `Regex`. Other interesting signatures are `Regex<JSONToken, JSONEnumeration>` or `Regex<HTTPRequestHeaderToken, HTTPRequestHeader>`. Building parsers becomes fun!
> 
> - George
> 
>> On Jan 10, 2018, at 11:58 AM, Michael Ilseman via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> Hello, I just sent an email to swift-dev titled "State of String: ABI, Performance, Ergonomics, and You!” at https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20180108/006407.html <https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20180108/006407.html>, whose gist can be found at https://gist.github.com/milseman/bb39ef7f170641ae52c13600a512782f <https://gist.github.com/milseman/bb39ef7f170641ae52c13600a512782f>. I posted to swift-dev as much of the content is from an implementation perspective, but it also addresses many areas of potential evolution. Please refer to that email for details; here’s the recap from it:
>> 
>> ### Recap: Potential Additions for Swift 5
>> 
>> * Some form of unmanaged or unsafe Strings, and corresponding APIs
>> * Exposing performance flags, and some way to request a scan to populate them
>> * API gaps
>> * Character and UnicodeScalar properties, such as isNewline
>> * Generalizing, and optimizing, String interpolation
>> * Regex literals, Regex type, and generalized pattern match destructuring
>> * Substitution APIs, in conjunction with Regexes.
>> 
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> 
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