I recently decided to look at Perl, and when faced with Perl 5 vs 6, I went with 5 due to its maturity and vast support.
However, one of the features of Perl 6 which really intrigued me was the
keyword, allowing one to define a language grammar which can be used to parse complex text. In other languages either an external library or a manual parsing implementation is usually needed for this.
Now that I've settled on Perl 5, is there any rough equivalent to Perl 6's
keyword in Perl 5 (or other functionality for building grammars), built-in or otherwise?