dsl_arithmetic_5_optimize_op_implementation.h

template<typename Tag, typename Step>
expression optimize_op(op<Tag, expression> const& e, int neutral, Step step)
{
   int res = neutral;
   std::vector<expression> subs;
   
   for (expression const& sub: e.rands())
   {
      if (auto* i = get_as_cst(sub.get()))
      {
         res = step(res, *i);
      }
      else
      {
         subs.push_back(sub);
      }
   }
   
   if (subs.empty()) return cst(res);
   if (res != neutral) subs.push_back(cst(res));
   if (subs.size() == 1) return subs.front();
   return expression(op<Tag, expression>(subs));
}

template<typename Range>
bool has_zero(Range const& subs)
{
   return end(subs) != boost::find_if(subs, [](expression const& sub) {
      auto* i = get_as_cst(sub.get());
      return i && *i == 0;
   });
}