[krick]

It might be applied (but this isn't the only possible approach, and I rarely use parser combinators) every time you need to write a parser. And when you need to write a parser? Oh, I have to write parsers all the time, seriously. It's not like all data is passed using json or something like this nowadays, there're plenty domains where obscure, custom data formats (often intended primarily to be read by humans, not processed by machines) are used. So when you need to use such a system with a custom data format you ought to write your own parser.