Data Types of Semantic Values
-----------------------------

   In a simple program it may be sufficient to use the same data type
for the semantic values of all language constructs.  This was true in
the RPN and infix calculator examples (*note Reverse Polish Notation
Calculator: RPN Calc.).

   Bison's default is to use type `int' for all semantic values.  To
specify some other type, define `YYSTYPE' as a macro, like this:

     #define YYSTYPE double

This macro definition must go in the C declarations section of the
grammar file (see Outline of a Bison Grammar: Grammar Outline.).