I talked to an older computer science professor today. He showed me compilers he had written in C that compiled a language he had made to assembly. He had never heard of Perl. He seemed astonished when I showed him one line of Perl that demonstrated recursive descent parsing.

I am not attempting to denigrate his compiler, which was awesome. I aim only to share a story of a seeming anachronism.

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Re: Perl Parsing Power
by BrowserUk (Patriarch) on Sep 24, 2012 at 10:09 UTC
    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.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

    RIP Neil Armstrong
[reply]
      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]

        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: Perl Parsing Power
by locked_user sundialsvc4 (Abbot) on Sep 24, 2012 at 13:07 UTC

    I think that he was being polite to you ...

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