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Xue Yong Zhi recently released rubyfront, which is already able to parse all the Ruby code included in the stable snapshot and the >70KLocs of Ruby on Rails (btw. things have changed a fair deal since that "riding a 1Kloc framework" talk). I've been providing some unusual syntax samples to chew on.

This is part of the activity in the Grammarians mailing list, where a bunch of courageous Rubyists*1 are struggling to build a stand-alone Ruby parser, while a few others (like me) throw ugly constructions at them.

Here are some of the things I found in the wild, loosely sorted so the most common come first (I could feed them to my lexical complexity estimator for Ruby, but that's too much work).

Naughty regexps

Seen in Getopt:

while self.sub!(/(^|\n)([^\t\n]*)(\t+)/sex) { |f|
 ...
}

%s literals

I hadn't seen that many before:

foo = %s'some symbol!($)!!'                        # => :"some symbol!($)!!"

Found in Borges.

_ separators after the decimal point

Seen in Extmath:

C = 0.577_215_664_901_532_861

rescue on non-constant expressions