Class Expr

gil/gil.impl.hpp:387–413

namespace _impl_ {

template <auto op, typename... Args> struct Expr {
  template <typename Runtime>
  using Eval = decltype(op(typename Args::template Eval<Runtime>{}...));

#define UN_OP(O)                                                               \
  constexpr auto operator O() const noexcept {                                 \
    return Expr<[](auto self) { return O self; }, Expr<op, Args...>>{};        \
  }
#define POST_UN_OP(O)                                                          \
  constexpr auto operator O##O(int) const noexcept {                           \
    return Expr<[](auto self) { return self O##O; }, Expr<op, Args...>>{};     \
  }
#define BIN_OP(O)                                                              \
  template <typename Rhs> constexpr auto operator O(Rhs) const noexcept {      \
    return Expr<[](auto self, auto rhs) { return (self O rhs); },              \
                Expr<op, Args...>, Rhs>{};                                     \
  }
#define POLY_OP(O)                                                             \
  template <typename... Rhs>                                                   \
  constexpr auto operator O(Rhs...) const noexcept {                           \
    return Expr<[](auto self, auto... rhs) {                                   \
      return self.operator O(rhs...);                                          \
    },                                                                         \
                Expr<op, Args...>, Rhs...>{};                                  \
  }
#include "ops.inc"
};

constexpr auto id = [](auto x) { return x; };
template <typename E> static constexpr auto expr = Expr<id, E>{};