YACC(1) YACC(1) NAME yacc, eyacc - yet another compiler-compiler SYNOPSIS yacc [ -vdD ] [ -o output ] [ -s stem ] grammar eyacc [ -v ] [ grammar ] DESCRIPTION Yacc converts a context-free grammar into a set of tables for a simple automaton which executes an LR(1) parsing algo- rithm. 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. The output file name can be set with the -o flag. 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 -D flag is given, yacc creates y.debug, which con- tains default error messages for the parser. The parser will use them if it is compiled with the preprocessor symbol YYDEBUG defined. The amount of diagnostic output is con- trolled by an external variable yydebug. If it is 2, the parser prints out the name of each token returned by yylex and each reduction. If it is 1, the parser prints out the reductions, and if it is 0, the parser only reports errors. 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. The prefix y. for the files y.tab.c y.tab.h, y.debug, and y.output can be changed to stem by the -s flag. Eyacc is an old version of yacc, with systematic error recovery. It is used in pascal(1). FILES y.output y.tab.c YACC(1) YACC(1) y.tab.h defines for token names y.debug y.tmp.?????? temporary file y.acts.????? temporary file /usr/lib/yaccparparser prototype for C programs /lib/liby.a library with default `main' and `yyerror' SEE ALSO lex(1) LR Parsing by A. V. Aho and S. C. Johnson, Computing Sur- veys, June, 1974. YACC - Yet Another Compiler Compiler by S. C. Johnson. Susan L. Graham, Charles B. Haley, and W. N. Joy, Practical LR Error Recovery, SIGPLAN Conference on Compiler Construc- tion, August, 1979. DIAGNOSTICS 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. BUGS The parser may not have full information when it prints out y.debug so that the names of the tokens returned by yylex may be missing.