1. Default argument
Kei Hasegawa

2. Not a type Bellow codes are error:
typedef void FUNC(int = 1);
void (*pf)(int = 2);
See ISO/IEC Default arguments
So, bellow implementation is incorrect:
class default_arg_type : public type {
const type* m_T;
var* m_default_arg; // default argument
... };

3. Example of implementation
struct usr : var {
enum flag_t { ..., HAS_DEFAULT_ARG, ... };
flag_t m_flag; };
map<usr*, vector<var*> > default_arg_table;
Maintain default arguments. A key of this table is function.
usr* u = ...
usr::flag_t flag = u->m_flag;
if (flag & usr::HAS_DEFAULT_ARG) {
p = default_arg_table.find(u);
vecotr<var*>& v = p->second;
... }