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Re^2: Perl Parsing Power

by protist (Monk)
on Sep 24, 2012 at 10:21 UTC ( #995343=note: print w/ replies, xml ) Need Help??


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))*+})/;
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 (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

    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

      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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