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in reply to Re: Perl Parsing Power
in thread Perl Parsing Power

Admittedly, it is a basic example, although powerful in its implications. 
print "good string\n" if $_~~ /^({(?:[^{}]++|(?1))*+})/;

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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))*+})/;'

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Re^3: Perl Parsing Power
by BrowserUk (Patriarch) 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

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    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
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[d/l]

      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.

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