The Purdue Compiler Construction Tool Set (PCCTS).
PCCTS consists of ANother Tool for Language Recognition (ANTLR), a
DFA-based Lexical analyzer Generator (DLG) and assorted other utilities
designed for the construction of compilers and other language translators.
ANTLR is a parser generator which generates recursive descent parsers which
are easier to debug than the table driven bottom-up parsers created by YACC.
It also provides support for the automatic generation of Abstract Syntax
Trees (AST's).
Many projects have stopped using PCCTS and moved on to antlr, which is
also packaged for Debian. New projects should probably look there first.
However PCCTS will be maintained in Debian as long as there is interest in
doing so.