Compilers: Principles and Practice by Pearson

152 Compilers – Principles and Practice

char s; /* symbol table index */

Node *np; /* node pointer */

};

This results in the following code being included in the yacc output header file y.tab.h:

typedef union {

int i; /* integer value */

float f; /* float value */

char s; /* symbol table index */

Node *np; /* node pointer */

} YYSTYPE;

extern YYSTYPE yylval;

The type of semantic value for each type of term in the grammar is defined at the beginning of the

yacc input file as:

%token <i> INTEGER

%type <f> expr

This binds expr to f, and INTEGER to i in the YYSTYPE union. With this binding, yacc

automatically generates a correct ...