lexer generator for C, C++, Go and Rust

 re2c's main goal is generating fast lexers: at least as fast as
 their reasonably optimized hand-coded counterparts. Instead of using
 a traditional table-driven approach, re2c encodes the generated
 finite state automata directly in the form of conditional jumps and
 comparisons. The resulting programs are faster and often smaller
 than their table-driven analogues, and they are much easier to debug
 and understand. Quite a few optimizations are applied in order to
 speed up and compress the generated code.
 .
 Another distinctive feature is its flexible interface: instead of
 assuming a fixed program template, re2c lets the programmer write
 most of the interface code and adapt the generated lexer to any
 particular environment.