Manual

Chapter 4: Parser C-Language Interface 63
4 Parser C-Language Interface
The Bison parser is actually a C function named yyparse. Here we describe the interface
conventions of yyparse and the other functions that it needs to use.
Keep in mind that the parser uses many C identifiers starting with ‘yy’ and ‘YY’ for
internal purposes. If you use such an identifier (aside from those in this manual) in an
action or in epilogue in the grammar file, you are likely to run into trouble.
4.1 The Parser Function yyparse
You call the function yyparse to cause parsing to occur. This function reads tokens,
executes actions, and ultimately returns when it encounters end-of-input or an unrecoverable
syntax error. You can also write an action which directs yyparse to return immediately
without reading further.
int yyparse (void)
[Function]
The value returned by yyparse is 0 if parsing was successful (return is due to end-ofinput).
The value is 1 if parsing failed because of invalid input, i.e., input that contains a
syntax error or that causes YYABORT to be invoked.
The value is 2 if parsing failed due to memory exhaustion.
In an action, you can cause immediate return from yyparse by using these macros:
YYACCEPT
Return immediately with value 0 (to report success).
YYABORT
Return immediately with value 1 (to report failure).
[Macro]
[Macro]
If you use a reentrant parser, you can optionally pass additional parameter information
to it in a reentrant way. To do so, use the declaration %parse-param:
%parse-param {argument-declaration}
[Directive]
Declare that an argument declared by the braced-code argument-declaration is an additional
yyparse argument. The argument-declaration is used when declaring functions
or prototypes. The last identifier in argument-declaration must be the argument
name.
Here’s an example. Write this in the parser:
%parse-param {int *nastiness}
%parse-param {int *randomness}
Then call the parser like this:
{
int nastiness, randomness;
... /* Store proper data in nastiness and randomness. */
value = yyparse (&nastiness, &randomness);
...
}
In the grammar actions, use expressions like this to refer to the data: