Yacc

 ( Compiling Tools ) 

Yacc was originally written in the B programming language, but was soon rewritten in C by Alan Snyder. It appeared as part of Version 3 Unix, and a full description of Yacc was published in 1975.

Johnson used Yacc to create the Portable C Compiler. Bjarne Stroustrup also attempted to use Yacc to create a formal specification of C++, but "was defeated by C's syntax". While finding it unsuitable for a formal specification of the language, Stroustrup did proceed to use Yacc to implement Cfront, the first implementation of C++.

In a 2008 interview, Johnson reflected that "the contribution Yacc made to the spread of Unix and C is what I'm proudest of".

Yacc produces only a parser (phrase analyzer) which can be used alone in the case of scannerless parsing however, full syntactic analysis typically requires an external lexical analyzer to perform a tokenization stage first (word analysis), which is then followed by the parsing stage proper. Lexical analyzer generators, such as Lex or Flex, are widely available for this purpose. The IEEE POSIX P1003.2 standard defines the functionality and requirements for both Lex and Yacc., .

Some versions of AT&T Yacc have become open source. For example, source code is available with the standard distributions of Plan 9.

Yacc was also one of several UNIX tools available for Charles River Data Systems' UNOS operating system under Bell Laboratories license.

Among the languages that were first implemented with Yacc are AWK, C++, eqn and Pic language. Yacc was also used on Unix to implement the Portable C Compiler, as well as parsers for such programming languages as FORTRAN 77, Ratfor, APL, bc, m4, etc.