Text Processing with Ruby

Chapter 10Writing Parsers

Sometimes regular expressions can get a little hairy. Once you begin using lots of lookahead assertions, have many capture groups, and generally have a regular expression that’s getting a bit scary to look at, it’s probably a sign that you’re trying to do too much in a single expression. Some problems are also just plain impossible to solve with a regular expression, so an alternative isn’t only desirable, but is also actually necessary. We saw one such example in Chapter 6, ​Scraping HTML​, when thinking about how to handle HTML.

In that case and many others, the best approach is to write a parser. A parser generally steps through a piece of text bit by bit, building up information as it goes and deciding what action ...