eis/mix_cc/matheval/evaluator.cpp

#define MATHEVAL_IMPLEMENTATION

#include "evaluator.hpp"
#include "ast.hpp"

namespace mix_cc {

namespace matheval {

namespace ast {

// Optimizer

template <typename T>
struct holds_alternative_impl {
  using result_type = bool;

  template <typename U>
  bool operator()(U const&) const {
    return std::is_same<U, T>::value;
  }
};

template <typename T, typename... Ts>
bool holds_alternative(x3::variant<Ts...> const& v) {
  return boost::apply_visitor(holds_alternative_impl<T>(), v);
}

ConstantFolder::result_type ConstantFolder::operator()(nil) const {
  return result_type{0};
}

ConstantFolder::result_type ConstantFolder::operator()(double n) const {
  return result_type{n};
}

ConstantFolder::result_type ConstantFolder::operator()(
    std::string const& c) const {
  return result_type{c};
}

ConstantFolder::result_type ConstantFolder::operator()(
    operation const& x, operand const& lhs) const {
  auto rhs = boost::apply_visitor(*this, x.rhs);

  if (holds_alternative<double>(lhs) && holds_alternative<double>(rhs)) {
    return result_type{x.op(boost::get<double>(lhs), boost::get<double>(rhs))};
  }
  return result_type{binary_op{x.op, lhs, rhs}};
}

ConstantFolder::result_type ConstantFolder::operator()(
    unary_op const& x) const {
  auto rhs = boost::apply_visitor(*this, x.rhs);

  /// If the operand is known, we can directly evaluate the function.
  if (holds_alternative<double>(rhs)) {
    return result_type{x.op(boost::get<double>(rhs))};
  }
  return result_type{unary_op{x.op, rhs}};
}

ConstantFolder::result_type ConstantFolder::operator()(
    binary_op const& x) const {
  auto lhs = boost::apply_visitor(*this, x.lhs);
  auto rhs = boost::apply_visitor(*this, x.rhs);

  /// If both operands are known, we can directly evaluate the function,
  /// else we just update the children with the new expressions.
  if (holds_alternative<double>(lhs) && holds_alternative<double>(rhs)) {
    return result_type{x.op(boost::get<double>(lhs), boost::get<double>(rhs))};
  }
  return result_type{binary_op{x.op, lhs, rhs}};
}

ConstantFolder::result_type ConstantFolder::operator()(
    expression const& x) const {
  auto state = boost::apply_visitor(*this, x.lhs);
  for (operation const& oper : x.rhs) {
    state = (*this)(oper, state);
  }
  return result_type{state};
}

// Evaluator

double eval::operator()(nil) const {
  BOOST_ASSERT(0);
  return 0;
}

double eval::operator()(double n) const { return n; }

double eval::operator()(std::string const& c) const {
  auto it = st.find(c);
  if (it == st.end()) {
    throw std::invalid_argument("Unknown variable " + c);  // NOLINT
  }
  return it->second;
}

double eval::operator()(operation const& x, double lhs) const {
  double rhs = boost::apply_visitor(*this, x.rhs);
  return x.op(lhs, rhs);
}

double eval::operator()(unary_op const& x) const {
  double rhs = boost::apply_visitor(*this, x.rhs);
  return x.op(rhs);
}

double eval::operator()(binary_op const& x) const {
  double lhs = boost::apply_visitor(*this, x.lhs);
  double rhs = boost::apply_visitor(*this, x.rhs);
  return x.op(lhs, rhs);
}

double eval::operator()(expression const& x) const {
  double state = boost::apply_visitor(*this, x.lhs);
  for (operation const& oper : x.rhs) {
    state = (*this)(oper, state);
  }
  return state;
}

}  // namespace ast

}  // namespace matheval

}  // namespace mix_cc