Yacc (for "yet another compiler compiler." ) is the standard parser generator for the Unix operating system. An open source program, yacc generates code for the parser in the C programming language. The acronym is usually rendered in lowercase but is occasionally seen as YACC or Yacc. The original version of yacc was written by Stephen Johnson at American Telephone and Telegraph (AT&T). Versions of yacc have since been written for use with Ada, Java and several other less well-known programming languages.