Ad hoc C++ generation

out-c++-example.lisp

CL-USER> (defmacro c++ (&rest args)
           `(constantia:out
             (:use smack/backend/c++-out:*c++-out-dispatch-table*)
             (:to (make-instance 'constantia:indenting-stream :stream *standard-output*))
             ,@args))
C++
CL-USER> (c++ (:include "iostream" :system)
              (:fndef "main" () "int"
                      "std::cout << \"hi\";" (:%)
                      (:return 0)))
#include <iostream>
int main()
{
  std::cout << "hi";
  return 0;
}