Metalang99 is a firm foundation for writing reliable and maintainable metaprograms in pure C99. It is implemented as an interpreted FP language atop of preprocessor macros: just #include <metalang99.h> and you are ready to go. Metalang99 features algebraic data types, pattern matching, recursion, currying, and collections; in addition, it provides means for compile-time error reporting and debugging. With our built-in syntax checker, macro errors should be perfectly comprehensible, enabling you for convenient development.