yacc – yet another compiler-compiler|
yacc [ option ... ] grammar|
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
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 generated by lex(1)),
with a main(int argc, char *argv) program, 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 messages. To incorporate
them in the parser, compile 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 transitions.
−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 statements 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
−l Disable #line directives in the generated parser.
−a Generate a parser that takes an argument of type Yyarg and passes
this argument to each invocation of the lexer function, yylex.
Yyarg contains per-instance state and a single user-visible member,
arg, of type void*.
The specification of yacc itself is essentially the same as the
UNIX version described in the references mentioned 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(7)), 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
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 Environment,
Prentice Hall, 1984
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.|