---
name: "plan9-yacc"
section: "1"
platform: "linux"
package: "9base"
version: "1:6-5"
release: "Debian 7 (Wheezy)"
platforms: ["linux"]
url: "https://new.carta.tech/plan9-yacc"
---

# plan9-yacc(1)

yet another compiler-compiler

## 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 This program must be loaded with a lexical analyzer function, **yylex(void)** (often generated by [*lex*(1)](/lex/1.md)), 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**.

- **-D***n*

  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 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.

- **-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 structure.

## FILES

- **y.output**

  - **y.tab.c**

  - **y.tab.h**

  - **y.debug**

  - **y.tmp.\***

  temporary file

- **y.acts.\***

  temporary file

- **/lib/yaccpar**

  parser prototype

- **/lib/yaccpars**

  parser prototype using stdio

## SOURCE

**/src/cmd/yacc.c**

## SEE ALSO

[*lex*(1)](/lex/1.md)\
 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

## BUGS

The parser may not have full information when it writes to **y.debug** so that the names of the tokens returned by may be missing.