There're a lot of line-based formats in bioinformatics which can be described
with some regular language. You can parse them with regular expressions from
your favourite dynamic language but that's not effective. Ragel takes a formal
grammar of the language, makes state machine for you, and allows you to
insert actions (snippets of code in C/C++, Objective C, Java, Ruby, D, or Go) in 
state transitions. 

How to use: 
    * install Ragel if you haven't done it yet
    * copy file with grammar description for your format
    * modify it: add some actions (read Ragel User Guide to learn how to do it)
    * produce source code
    * enjoy its performance and robustness ;-)