How do modules compose with respect to syntax? I remember encountering a big frustration in Common Lisp when I used two libraries that depended on defining '[' as a reader macro for pretty syntax. Whichever library I allowed to use the '[' reader macro, my usage of the other library became verbose and hard to read.

Not to mention that neither altering a module's source nor depending on the sequence of module loading is scalable across many modules.

And people wonder why Perl is known as a "write-only" language!

Rails is running into the same problem with overuse/abuse of monkey patching, method_missing etc. that perl ran into with overuse/abuse of rich syntax.

It's sad. But it's really nothing to do with either language. They just handed a large chunk of power to a developer community that grew too large too fast for most of the membership to have learned how to use that power responsibly.

Perl 6 has an advantage in that most of the tutorials and examples aren't full of bad examples and muddled thinking like most of the Perl 5 tutorials and examples are. I don't expect that to last, but hopefully some thoughtful language design will make abusing the language much more difficult.

Perl's not alone here, you can do the same thing with C++ using operator overloading, but Perl actively encourages this to an order of magnitude greater extent.