dsl_arithmetic_5_printer.h

template<typename Tag>
std::string print_op(op<Tag, std::string> const& e, std::string const& op_repr)
{
   return std::string("(") + op_repr + " " + boost::algorithm::join(e.rands(), " ") + ")";
}

std::string print_alg(expression_r<std::string> const& e)
{
   if (auto* o = get_as_add(e)) return print_op(*o, "+");
   if (auto* o = get_as_mul(e)) return print_op(*o, "*");
   if (auto* i = get_as_cst(e)) return std::to_string(*i);
   if (auto* v = get_as_var(e)) return *v;
   throw_missing_pattern_matching_clause();
}