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(bison.info)Token Values

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Semantic Values of Tokens
-------------------------

   In an ordinary (non-reentrant) parser, the semantic value of the
token must be stored into the global variable `yylval'.  When you are
using just one data type for semantic values, `yylval' has that type.
Thus, if the type is `int' (the default), you might write this in
`yylex':

       ...
       yylval = value;  /* Put value onto Bison stack. */
       return INT;      /* Return the type of the token. */
       ...

   When you are using multiple data types, `yylval''s type is a union
made from the `%union' declaration (Note: The Collection of Value
Types.).  So when you store a token's value, you must use
the proper member of the union.  If the `%union' declaration looks like
this:

     %union {
       int intval;
       double val;
       symrec *tptr;
     }

then the code in `yylex' might look like this:

       ...
       yylval.intval = value; /* Put value onto Bison stack. */
       return INT;          /* Return the type of the token. */
       ...