#define def decltype(auto)

def sum(int a, int b) {
    return a+b;
}

struct Compiler {
  using Builtin_binop = SSA_sequence(SSA_value, SSA_value);
  Builtin_binop emit_add, emit_sub, emit_mul, emit_div; // ...
};

SSA_sequence Compiler::emit_add(SSA_value a, SSA_value b) {
  return ...;
}

...

#define move(x) (*(new decltype(x)(x)))

void foo(int x) {
  if (x)
    my_label:
    switch (x)
      case 1:
      case 2:
      default:
        std::puts("gram.stmt");
}

  auto walk = [&](int i, int c, auto &&walk) {
        ...
        walk(input[i], c, walk);
    };