Manual

68 Bison 2.3
%pure-parser
%lex-param {int *nastiness}
/* Pure yyparse. */
%parse-param {int *nastiness}
%parse-param {int *randomness}
results in the following signatures for all the parser kinds:
int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
int yyparse (int *nastiness, int *randomness);
void yyerror (YYLTYPE *locp,
int *nastiness, int *randomness,
char const *msg);
The prototypes are only indications of how the code produced by Bison uses yyerror.
Bison-generated code always ignores the returned value, so yyerror can return any type,
including void. Also, yyerror can be a variadic function; that is why the message is always
passed last.
Traditionally yyerror returns an int that is always ignored, but this is purely for
historical reasons, and void is preferable since it more accurately describes the return type
for yyerror.
The variable yynerrs contains the number of syntax errors reported so far. Normally this
variable is global; but if you request a pure parser (see Section 3.7.10 [A Pure (Reentrant)
Parser], page 58) then it is a local variable which only the actions can access.
4.4 Special Features for Use in Actions
Here is a table of Bison constructs, variables and macros that are useful in actions.
$$
$n
[Variable]
Acts like a variable that contains the semantic value for the grouping made by the
current rule. See Section 3.5.3 [Actions], page 47.
[Variable]
Acts like a variable that contains the semantic value for the nth component of the
current rule. See Section 3.5.3 [Actions], page 47.
$$
[Variable]
Like $$ but specifies alternative typealt in the union specified by the %union declaration.
See Section 3.5.4 [Data Types of Values in Actions], page 48.
$n
[Variable]
Like $n but specifies alternative typealt in the union specified by the %union declaration.
See Section 3.5.4 [Data Types of Values in Actions], page 48.
YYABORT;
[Macro]
Return immediately from yyparse, indicating failure. See Section 4.1 [The Parser
Function yyparse], page 63.
YYACCEPT;
[Macro]
Return immediately from yyparse, indicating success. See Section 4.1 [The Parser
Function yyparse], page 63.