32v 1m yacc

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YACC(1) UNIX Programmer's Manual YACC(1)


yacc - yet another compiler-compiler


yacc [ -vd ] grammar


Yacc converts a context-free grammar into a set of tables for a simple automaton which executes an LR(1) parsing algorithm. The grammar may be ambiguous; specified precedence rules are used to break ambiguities.

The output file, y.tab.c, must be compiled by the C compiler to produce a program yyparse. This program must be loaded with the lexical analyzer program, yylex, as well as main and yyerror, an error handling routine. These routines must be supplied by the user; Lex(1) is useful for creating lexical analyzers usable by yacc.

If the -v flag is given, the file y.output is prepared, which contains a description of the parsing tables and a report on conflicts generated by ambiguities in the grammar.

If the -d flag is used, the file y.tab.h is generated with the define statements that associate the yacc-assigned `token codes' with the user-declared `token names'. This allows source files other than y.tab.c to access the token codes.


    y.tab.h             defines for token names
    yacc.tmp, yacc.acts temporary files
    /usr/lib/yaccpar    parser prototype for C programs
    /lib/liby.a         library with default `main' and `yyerror'


  • lex(1)
  • LR Parsing by A. V. Aho and S. C. Johnson, Computing Surveys, June, 1974.
  • YACC - Yet Another Compiler Compiler by S. C. Johnson.


The number of reduce-reduce and shift-reduce conflicts is reported on the standard output; a more detailed report is found in the y.output file. Similarly, if some rules are not reachable from the start symbol, this is also reported.


Because file names are fixed, at most one yacc process can be active in a given directory at a time.