typed_calc.swift

import Foundation

indirect enum Exp {
  case add(Exp, Exp)
  case sub(Exp, Exp)
  case num(Int)
  
  func apply() -> Int {
    switch self {
    case let .add(e1, e2):
      return e1.apply() + e2.apply()
    case let .sub(e1, e2):
      return e1.apply() - e2.apply()
    case let .num(n):
      return n
    }
  }
}

let e1 = Exp.add(
  .num(1),
  .sub(
    .num(2),
    .add(
      .add(
        .add(
          .num(2),
          .sub(
            .add(
              .num(3),
              .num(4)),
            .num(1)
          )
        ),
        .add(
          .num(2),
          .num(100)
        )
      ),
      .sub(
        .num(100),
        .num(101)
      )
    )
  )
 )

print(e1.apply())

/* 
Your previous C++ content is preserved below:

// This is a sandbox to experiment with CoderPad's execution capabilities.
// It's a temporary, throw-away session only visible to you.

#include <iostream>
using namespace std;

// To execute C++, please define "int main()"
int main() {
  auto words = { "Hello, ", "World!", "\n" };
  for (const string& word : words) {
    cout << word;
  }
  return 0;
}

 */