<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 24, 2017, at 10:14 AM, Chris Eidhof <<a href="mailto:chris@eidhof.nl" class="">chris@eidhof.nl</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Hey Matthew, <div class=""><br class=""></div><div class="">Do you have an example of doing parser combinators without FP? I'd be very interest</div></div></div></blockquote><div><br class=""></div><div>Hey Chris, looks like Dave provided a pretty good example of the kind of thing I was talking about. Does that answer your questions?</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="gmail_extra"><br class=""><div class="gmail_quote">On Tue, Jan 24, 2017 at 4:52 PM, Matthew Johnson <span dir="ltr" class=""><<a href="mailto:matthew@anandabits.com" target="_blank" class="">matthew@anandabits.com</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 24, 2017, at 2:05 AM, Chris Eidhof via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</div><br class="m_7759073561154812750Apple-interchange-newline"><div class=""><div dir="ltr" class="">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.<div class=""><br class=""></div><div class="">There are a couple of possibilities that come to mind directly:</div><div class=""><br class=""></div><div class="">1. Build parsers right into the language (like Perl 6 grammars)</div><div class="">2. Provide a parser combinator language (e.g. <a href="https://github.com/davedufresne/SwiftParsec" target="_blank" class="">https://github.com/<wbr class="">davedufresne/SwiftParsec</a>). </div><div class="">3. Rely on external tools like bison/yacc/etc.</div><div class="">4. Make it easy for people to write hand-written parsers (e.g. by providing an NSScanner alternative).</div><div class=""><br class=""></div><div class="">Some obvious drawbacks of each approach:</div><div class=""><br class=""></div><div class="">1. Lots of work, probably hard to get right?</div><div class="">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.</div></div></div></blockquote><div class=""><br class=""></div><div class="">FWIW, it is quite possible to do things very similar to parser combinators without functional programming. What you need is a way to create and compose small parser fragments, ideally an EDSL approaching something like EBNF that allows users to build a grammar out of the parser fragments, and a way to execute / interpret the resulting grammar during parsing. </div></div></div></blockquote><div class=""><br class=""></div><div class="">I'd love to see this. Do you mean "possible today" or "it would be possible”?</div></div></div></div></div></blockquote><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><div class=""><br class=""></div><div class="">One really big thing that I took away learning parser combinators is that grammars are composable, whereas parsers themselves are not. Parser combinators express grammars.</div><div class=""><br class=""></div><div class="">For example, when you have a Swift parser available, and you want to "embed" it inside a Markdown parser, that's hard to do. Whereas composing the Markdown grammar with the Swift grammar is a lot easier.</div><div class=""><br class=""></div><div class="">It'd be nice to have that composability.</div><div class=""><br class=""></div><div class="">Chris</div><div class=""> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><div class=""><div class=""><br class=""></div><div class="">The functional approach would not be the most idiomatic approach in Swift and as you note, it probably wouldn’t have the performance a more idiomatic approach could achieve (too much copying).</div><div class=""><br class=""></div><div class="">My intuition is that a hybrid 1 / 2 approach might be best: do as much as possible in the library and let the design drive new language enhancements where necessary.</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="">3. No clear integrated way to do this</div><div class="">4. You still have to know how to write a parser.</div><div class=""><br class=""></div><div class="">I would think that 4. would be a good step forward, and 1/2 would definitely benefit from this.</div><div class=""><br class=""></div><div class="">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 possibilities.</div></div><div class="gmail_extra"><br class=""><div class="gmail_quote">On Tue, Jan 24, 2017 at 8:46 AM, Russ Bishop via swift-evolution <span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><div class=""><div class="m_7759073561154812750h5"><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 23, 2017, at 2:27 PM, Joe Groff via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</div><br class="m_7759073561154812750m_-8874196560321488059Apple-interchange-newline"><div class=""><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class=""><blockquote type="cite" class=""><div class=""><br class="m_7759073561154812750m_-8874196560321488059Apple-interchange-newline">On Jan 23, 2017, at 2:06 PM, Ben Cohen via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</div><br class="m_7759073561154812750m_-8874196560321488059Apple-interchange-newline"><div class=""><div style="word-wrap:break-word" class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Jan 23, 2017, at 7:49 AM, Joshua Alvarado <<a href="mailto:alvaradojoshua0@gmail.com" target="_blank" class="">alvaradojoshua0@gmail.com</a>> wrote:</div><br class="m_7759073561154812750m_-8874196560321488059Apple-interchange-newline"><div class=""><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="">Taken from<span class="m_7759073561154812750m_-8874196560321488059Apple-converted-space"> </span><a href="http://nshipster.com/nsregularexpression/" target="_blank" class="">NSHipster</a>:</div><blockquote class="gmail_quote" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">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.</blockquote><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class=""><br class=""></div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="">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. </div></div></blockquote></div><br class=""><div class=""><br class=""></div><div class="">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.</div></div></div></blockquote><br class=""></div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="">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.</div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class=""><br class=""></div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="">-Joe</div><br class=""></div></blockquote><br class=""></div></div></div><div class="">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. </div><div class=""><br class=""></div><div class="">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).</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Russ</div><br class=""></div><span class=""><br class="">______________________________<wbr class="">_________________<br class="">
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