Manual

Chapter 10: C++ Language Interface 107
Use the two following directives to enable parser tracing and verbose error messages.
%debug
%error-verbose
Semantic values cannot use “real” objects, but only pointers to them.
// Symbols.
%union
{
int
ival;
std::string *sval;
};
The code between ‘%{’ and ‘%}’ after the introduction of the ‘%union’ is output in the ‘*.cc’
file; it needs detailed knowledge about the driver.
%{
# include "calc++-driver.hh"
%}
The token numbered as 0 corresponds to end of file; the following line allows for nicer error
messages referring to “end of file” instead of “$end”. Similarly user friendly named are
provided for each symbol. Note that the tokens names are prefixed by TOKEN_ to avoid
name clashes.
%token END 0 "end of file"
%token ASSIGN ":="
%token IDENTIFIER "identifier"
%token NUMBER "number"
%type exp "expression"
To enable memory deallocation during error recovery, use %destructor.
%printer { debug_stream ()