#define cat(a,b) cat2(a,b)
#define cat2(a,b) a##b

#define FOO 199
#define REQUIRED_FOO 200
#if FOO < REQUIRED_FOO

void cat(cat(FOO_is_,FOO),
    cat(_required_FOO_is_,REQUIRED_FOO))()
{
  #warning Busted!
}

#endif