[swift-evolution] (no subject)

John Siracusa siracusa at gmail.com
Fri Dec 11 10:52:38 CST 2015

Chris Lattner wrote:

> When introducing a feature like this, I think it would be useful to survey
> a range of popular languages (and yes, even perl ;-) to understand what
> facilities they provide and why (i.e. what problems they are solving) and
> synthesize a good swift design that can solve the same problems with a
> hopefully simple approach.

Travis Tilley wrote:

> ​Perl and Erlang are unique in that valid code in either language looks
> essentially like line noise. I'd rather take inspiration from languages
> like ruby, python, and elixir.​

Jokes aside, the ability to choose delimiters for strings and other
language constructs that surround some value is a huge boon to code

For example, RegExp literals in JavaScript:

var regex = /^\/usr\/local\//; // gross

An even simpler example, which applies to many languages: a string literal
that contains all of your possible string delimiters within it. This is not
an exotic thing in English.

message = "\"I don't like this,\" she said."; // nope
message = '"I don\'t like this," she said.';  // still nope

Then, of course, there's your escape character itself:

escapes = "Some escapes: \\n, \\t, \\a"; // sigh

There are many time-tested solutions to these syntactic/cosmetic problems.

* Different delimiters with different interpolation rules (e.g., single
quotes not honoring any backslash escapes and not doing variable

* Matched-pair delimiters that don't require anything to be escaped as long
as the delimiters are absent or matched within the string. (These alone
solve a huge range of problems.)

* Heredocs for long literals where you get to pick the end token.

* Heredocs modified by delimiters around the end token to control
interpolation within the long literal.

Which language looks like line noise now?

$messasge = q("I can't believe how nice this is," she said (quietly).);

$regex = qr(^/usr/local/);

$escapes = 'Some escapes: \n, \t, \a';

My take: once you use a language where you pretty much never have to
backslash-escape a character you can easily type to get it into a string,
it's really hard to go back.

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