This section shows how a parser generator can be used to facilitate the construction of the front end of a compiler. We shall use the LALR parser generator Yacc as the basis of our discussion, since it implements many of the concepts discussed in the previous two sections and it is widely available. Yacc stands for "yet another compiler-compiler," reflecting the popularity of parser generators in the early 1970s when the first version of Yacc was created by S. C. Johnson. Yacc is available as a command on the UNIX system, and has been used to help implement many production compilers.
A translator can be constructed using Yacc in the manner illustrated in Fig. 4.57. First, a file, say translate.y, containing a Yacc specification of the translator is prepared. The UNIX system command
yacc translate.y
