yacc

- yet another compiler-compiler

Synopsis

yacc [-dltVv] [-b file_prefix] [-Q [y | n]] 
      [-P parser] [-p sym_prefix] file

Description

The yacc command converts a context-free grammar into a set of tables for a simple automaton that executes an LALR(1) parsing algorithm. The grammar can 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 function 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. The lex(1) command is useful for creating lexical analyzers usable by yacc.

Options

The following options are supported:

-b file_prefix

Uses file_prefix instead of y as the prefix for all output files. The code file y.tab.c, the header file y.tab.h (created when -d is specified), and the description file y.output (created when -v is specified), is changed to file_prefix.tab.c, file_prefix.tab.h, and file_prefix.output, respectively.

-d

Generates the file y.tab.h with the #define statements that associate the yacc user-assigned “token codes” with the user-declared “token names”. This association allows source files other than y.tab.c to access the token codes.

-l

Specifies that the code produced in y.tab.c does not contain any #line constructs. This option should only be used after the grammar and the associated actions are fully debugged.

-p sym_prefix

Uses sym_prefix instead of yy as the prefix for all external names produced by yacc. The names affected include the functions yyparse(), yylex() and yyerror(), and the variables yylval, yychar and yydebug. (In the remainder of this section, the six symbols cited are referenced using their default names only as a notational convenience.) Local names can also be affected by the -p option. However, the -p option does not affect #define symbols generated by yacc.

-P parser

Allows you to specify the parser of your choice instead of /usr/share/lib/ccs/yaccpar. For example, you can specify:

example% yacc -P ~/myparser parser.y

-Q[y|n]

The -Qy option puts the version stamping information in y.tab.c. This allows you to know what version of yacc built the file. The -Qn option (the default) writes no version information.

-t

Compiles runtime debugging code by default. Runtime debugging code is always generated in y.tab.c under conditional compilation control. By default, this code is not included when y.tab.c is compiled. Whether or not the -t option is used, the runtime debugging code is under the control of YYDEBUG , a preprocessor symbol. If YYDEBUG has a non-zero value, then the debugging code is included. If its value is 0, then the code is not included. The size and execution time of a program produced without the runtime debugging code is smaller and slightly faster.

-v

Prepares the file y.output, which contains a description of the parsing tables and a report on conflicts generated by ambiguities in the grammar.

-V

Prints on the standard error output the version information for yacc.

Operands

The following operand is required:

file

A path name of a file containing instructions for which a parser is to be created.

Examples

Example 1 Accessing the yacc Library

Access to the yacc library is obtained with library search operands to cc. To use the yacc library main:

example% cc y.tab.c -ly

Both the lex library and the yacc library contain main. To access the yacc main:

example% cc y.tab.c lex.yy.c -ly -ll

This ensures that the yacc library is searched first, so that its main is used.

The historical yacc libraries have contained two simple functions that are normally coded by the application programmer. These library functions are similar to the following code:

#include <locale.h>
int main(void)
{
        extern int yyparse();

        setlocale(LC_ALL, "");

        /* If the following parser is one created by lex, the
           application must be careful to ensure that LC_CTYPE
           and LC_COLLATE are set to the POSIX locale.  */
        (void) yyparse();
        return (0);
}

#include <stdio.h>

int yyerror(const char *msg)
{
        (void) fprintf(stderr, "%s\n", msg);
        return (0);
}

Environment Variables

See environ(5) for descriptions of the following environment variables that affect the execution of yacc: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.

yacc can handle characters from EUC primary and supplementary codesets as one-token symbols. EUC codes can only be single character quoted terminal symbols. yacc expects yylex() to return a wide character (wchar_t) value for these one-token symbols.

Exit Status

The following exit values are returned:

0

Successful completion.

>0

An error occurred.

Files

y.output

state transitions of the generated parser

y.tab.c

source code of the generated parser

y.tab.h

header file for the generated parser

yacc.acts

temporary file

yacc.debug

temporary file

yacc.tmp

temporary file

yaccpar

parser prototype for C programs

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

lex(1), attributes(5), environ(5), standards(5)

Diagnostics

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

Notes

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

Users are encouraged to avoid using $ as part of any identifier name.