Re: Perl Parsing Power

He seemed astonished when I showed him one line of Perl that demonstrated recursive descent parsing.

Recursive descent parsing in one line of Perl; I'd like to see that?

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

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Comment on Re: Perl Parsing Power
Re^2: Perl Parsing Power by protist (Scribe) on Sep 24, 2012 at 10:21 UTC
Admittedly, it is a basic example, although powerful in its implications. `print "good string\n" if $_~~ /^({(?:[^{}]++\|(?1))+})/;` [download] It tests for proper nesting of brackets, anchored to the beginning of the line. You can try it out: `perl -ne 'print "good string\n" if $_~~ /^({(?:[^{}]++\|(?1))+})/;'` [download]	[reply] [d/l] [select]
Re^3: Perl Parsing Power by BrowserUk (Pope) on Sep 24, 2012 at 10:58 UTC
You can do that like this: `C:\test>perl -nE"my$t; /{/&&++$t or /}/&&--$t for split''; say $t ? $t + : 'good string'" {} good string {}} -1 {{}} good string {{}{}} good string {{}{}}} -1 {{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{}}}}}}}}}}}}}}}}}}}}}}}}}}}}} 11 {{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{}}}}}}}}}}}}}}}}}}}}}}}}}} 14 {{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{}}}}}}}}}}}}}}}}}}}}}}}}}}}}}} +}}}} 6 {{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{}}}}}}}}}}}}}}}}}}}}}}}}}}}}}} +}}}}}}}}}} good string` [download] But I wouldn't call it RDP :) The problem with doing RDP with regex is that you have to match the entire stream with one (possibly (hopefully :) composite) regex. Which is fine for yes/no booleans, but it makes both debugging the regex and reporting where and why parsing errors occur extremely messy if not impossible. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. RIP Neil Armstrong	[reply] [d/l]
Re^4: Perl Parsing Power by protist (Scribe) on Sep 24, 2012 at 11:16 UTC
Unless I am mistaken, your oneliner will fail if given `}}}{{{` as input. It will report a false positive. It is also not RDP, although you know this ;). While I will not claim that regex RDP is pretty (complex parsing rarely is), it is possible, and Programming Perl discusses it in some minimal detail.	[reply] [d/l]


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Re: Perl Parsing Power

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