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In most programs, you will need different data types for different kinds
of tokens and groupings. For example, a numeric constant may need type
int
or long int
, while a string constant needs type
char *
, and an identifier might need a pointer to an entry in the
symbol table.
To use more than one data type for semantic values in one parser, Bison requires you to do two things:
%union
Bison declaration (see The Union
Declaration);
%define
variable api.value.type
to be a union type
whose members are the type tags (see Providing a
Structured Semantic Value Type);
typedef
or a #define
to define YYSTYPE
to be a
union type whose member names are the type tags.
%token
Bison declaration (see Token Type Names)
and for groupings with the %type
Bison declaration (see Nonterminal Symbols).