  We present two novel approaches to parsing context-free languages. The first
approach is based on an extension of Brzozowski's derivative from regular
expressions to context-free grammars. The second approach is based on a
generalization of the derivative to parser combinators. The payoff of these
techniques is a small (less than 250 lines of code), easy-to-implement parsing
library capable of parsing arbitrary context-free grammars into lazy parse
forests. Implementations for both Scala and Haskell are provided. Preliminary
experiments with S-Expressions parsed millions of tokens per second, which
suggests this technique is efficient enough for use in practice.
