Perl 6 - the future is here, just unevenly distributed

IRC log for #marpa, 2015-12-30

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Time Nick Message
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02:48 Topic for #marpa is now Start here: http://savage.net.au/Marpa.html - Pastebin: http://scsys.co.uk:8002/marpa - Jeffrey's Marpa site: http://jeffreykegler.github.io/Marpa-web-site/ - IRC log: http://irclog.perlgeek.de/marpa/today
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04:56 ronsavage I've had a idea. It'd be nice to write some sort of (perhaps partial) interface between the GIMP, IrfanView and the Perl modules Imager and Image::Magick. I can image how to do this, so I'll spell out some things in an article. As the intermediary language, the obvious choices are InfranView's macro language and Image::Magick's command line options (for 'convert'). More later.....
05:11 ronsavage Ahh. IrfanView uses its menu system so the user can define the steps. I can't find any docs about command line options for running the program in batch mode.
05:30 ronsavage And I think I'll leave Script-Fu (used by the GIMP via Gimp::Fu) for another day.
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16:18 Idiosyncrat https://wendyga.wordpress.com/2015/12/25/why​-would-you-want-to-use-perl-6-some-answers/
16:18 Idiosyncrat I note here the line about Perl 6 grammars, "which Perl 6 uses to parse itself"
16:20 Idiosyncrat That is not really true -- to the extent it suggests a feature that a Perl 6 adopter could use, it is certainly false.
16:21 Idiosyncrat The Perl 6 grammar in Perl 6 is a reference grammar -- I think (I'm not sure) that there is a way to actually parse Perl 6 using it,
16:21 Idiosyncrat but it is not used in the Perl 6 implementation.
16:22 Idiosyncrat Contrast Marpa's SLIF, which is not just described by a SLIF grammar, but which is parsed by one every time you use it --
16:23 Idiosyncrat there is no available way to parse the SLIF except via its self-describing grammar.
16:24 Idiosyncrat The question is whether Perl 6 grammars are a useful way to deal with languages as large and complex as Perl 6.
16:24 Idiosyncrat Right now there is no evidence that they are.
16:25 Idiosyncrat Someday the Perl 6 grammar may parse Perl 6, but even then the amount of time & talent it took to get it to parse a language ...
16:26 Idiosyncrat where the language was expressly designed to be parsed by Perl 6 grammars ...
16:27 Idiosyncrat suggests that Perl 6's self-parsing is essentially only theoretical.
16:27 Idiosyncrat What can Perl 6 grammars do?
16:28 Idiosyncrat I think it's reasonable to position them in the same way that Roberto Ierusalimschy positions his Lua PEG implementation --
16:29 Idiosyncrat as an extension of regular expressions.
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20:38 Idiosyncrat http://blogs.perl.org/users/jt_smith/2​015/12/christmas-came-bah-humbug.html
20:38 Idiosyncrat This pushes Perl 6 grammars as a "killer" features of the language.
20:40 Idiosyncrat Though there's no practical evidence they can deliver -- the Advent post for example, reproduced a toy subset of the SLIF and left recreating the rest of it as an exercise to the reader.
20:43 Idiosyncrat It also ignores the theoretical reasons that suggest that the Advent post author was wise not to spend time following up on his subset
20:44 Idiosyncrat The theoretical reasons: http://jeffreykegler.github.io/Ocean-of-Aware​ness-blog/individual/2015/12/composable.html
20:45 Idiosyncrat and http://jeffreykegler.github.io/Ocean-of-Awa​reness-blog/individual/2015/12/topdown.html
20:45 Idiosyncrat and http://jeffreykegler.github.io/Ocean-of-A​wareness-blog/individual/2015/03/peg.html
20:46 Idiosyncrat With some much else going for them, I am surprised the Perl 6 team wants, at his crucial time, to risk their credibility in this way.
20:47 Idiosyncrat s/some much else/so much else/
20:47 Idiosyncrat s/his crucial time/this crucial time/
20:48 Idiosyncrat That is, the rest of their vision, it is reasonable to believe that they have delivered on ...
20:49 Idiosyncrat or at least, if there are initial gotchas, these are fixable.
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21:41 ronsavage JK: What should a user of Marpa::R2 do when the ambiguity_metric is <= 0? See https://github.com/ronsavage/G​enealogy-Gedcom-Date/issues/1.
22:44 Idiosyncrat Currently all failures -- except calling ambiguity_metric before parsing on which 0 is returned -- are thrown.
22:44 Idiosyncrat So a return of 0 will usually be an unexpected fatal error.
22:45 Idiosyncrat And a return <0 a *really* unexpected fatal error.
22:46 Idiosyncrat In the case of the issue, I think it means you're calling ambiguity_metric when you shouldn't.
22:55 Idiosyncrat Specifically, 0 is what you'll see if you ask for an ambiguity metric of the parse when you haven't done any parsing yet.
23:10 Idiosyncrat OK, I looked some more.
23:11 Idiosyncrat A return of zero means "No parse".  ambiguity_metric() IIRC should be a reasonable way of detecting "No parse".
23:12 Idiosyncrat The documentation, while 100% correct, is not as clear as it could be about some these failure conditions.

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