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Syntax: bf(%stype typename) nl()
This directive defines the type of the semantic value of tokens. The
specified type must be a default constructible type, like tt(size_t) or
tt(std::string). By default, b() uses tt(int) for the semantic value type of
its parser's tokens. To use another single semantic value type , this
directive must be used.
In programs using a simple grammar it may be sufficient to use the same data
type for the semantic values of all language constructs (see, e.g., sections
ref(RPN) and ref(CALC)).
Any text following tt(%stype) up to the end of the line, up to the first
of a series of trailing blanks or tabs or up to a comment-token (tt(//) or
tt(/*)) becomes part of the type definition. Be sure em(not) to end a
tt(%stype) definition in a semicolon.
tt(%stype, %union) and tt(%polymorphic) are mutually exclusive: only one
of these directives can be used.
Sources including the generated parser class header file should refer to the
semantic value typename as bf(STYPE_).
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