YACC(1) YACC(1) NAME yacc - yet another compiler-compiler SYNOPSIS yacc [ option ... ] grammar DESCRIPTION Yacc converts a context-free grammar and translation code into a set of tables for an LR(1) parser and translator. 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 a lexical analyzer function, yylex(void) (often gener- ated by lex(1)), with a main(int argc, char *argv) pro- gram, and with an error handling routine, yyerror(char*). The options are -o output Direct output to the specified file instead of y.tab.c. -Dn Create file y.debug, containing diagnostic mes- sages. To incorporate them in the parser, com- pile it with preprocessor symbol yydebug defined. The amount of diagnostic output from the parser is regulated by value n. The value 0 reports errors; 1 reports reductions; higher values (up to 4) include more information about state tran- sitions. -v Create file y.output, containing a description of the parsing tables and of conflicts arising from ambiguities in the grammar. -d Create file y.tab.h, containing #define state- ments that associate yacc-assigned `token codes' with user-declared `token names'. Include it in source files other than y.tab.c to give access to the token codes. -s stem Change the prefix `y' of the file names y.tab.c, y.tab.h, y.debug, and y.output to stem. -S Write a parser that uses Stdio instead of the print routines in libc. The specification of yacc itself is essentially the same as the UNIX version described in the references mentioned YACC(1) YACC(1) below. Besides the -D option, the main relevant differences are: The interface to the C environment is by default through <libc.h> rather than <stdio.h>; the -S option reverses this. The parser accepts UTF input text (see utf(6)), which has a couple of effects. First, the return value of yylex() no longer fits in a short; second, the starting value for non-terminals is now 0xE000 rather than 257. The generated parser can be recursive: actions can call yyparse, for example to implement a sort of #include statement in an interpreter. Finally, some undocumented inner workings of the parser have been changed, which may affect programs that know too much about its structure. FILES y.output y.tab.c y.tab.h y.debug y.tmp.* temporary file y.acts.* temporary file /sys/lib/yaccpar parser prototype /sys/lib/yaccpars parser prototype using stdio SOURCE /sys/src/cmd/yacc.c SEE ALSO lex(1) S. C. Johnson and R. Sethi, ``Yacc: A parser generator'', Unix Research System Programmer's Manual, Tenth Edition, Volume 2 B. W. Kernighan and Rob Pike, The UNIX Programming Environ- ment, Prentice Hall, 1984 BUGS The parser may not have full information when it writes to y.debug so that the names of the tokens returned by `yylex' may be missing.