OMeta — a new object-oriented language for pattern matching. OMeta is based on a variant of Parsing Expression Grammars (PEGs) [5]—a recognition-based foundation for describing syntax—which we have extended to handle arbitrary kinds of data. We show that OMeta’s general-purpose pattern matching provides a natural and convenient way for programmers to implement tokenizers, parsers, visitors, and tree transformers, all of which can be extended in interesting ways using familiar object-oriented mechanisms. This makes OMeta particularly well-suited as a medium for experimenting with new designs
for programming languages and extensions to existing languages.

meta E {
  dig ::= ’0’ | ... | ’9’;
  num ::= <dig>+;
  fac ::= <fac> ’*’ <num>
    | <fac> ’/’ <num>
    | <num>;
  exp ::= <exp> ’+’ <fac>
    | <exp> ’-’ <fac>
    | <fac>;
}