Regex, Part 2: Compiler
What are Type-2 (or regular) languages? How can Finite State Automation be used to recognize them? Where do regex fit into all this?
Regex, Part 1: Parser
Exploring Parser Combinators (or monadic parsers) which are a great example of functional programming used to bring practical benefits
How to solve it without Coordinators and why Coordinators might be not an optimal solution for you