Definitely a very good introduction for the very uninitiated since it not only describes the concepts of source filtering but also shows some code examples. One topic I thought that was notably missing though is the how difficult it is to modify the actual language. For example I've been working on Sub::Lexical on and off for the past couple of months and have found that it's pretty much impossible to cover every base when filtering perl. As merlyn has said many times in the past only perl can parse Perl. While most filters don't need knowledge of the whole language's syntactic structure there are so many areas in which a simple s/// just won't cut it. Perhaps source filtering isn't meant to be used for such purposes which I have in mind, but it does seem prime for adding that favourite language feature from blub ...
HTH

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broquaint