is_leap_year.cc

#include <iostream>
#include <vector>

auto continuation = [](auto && val){return [=](auto && cont) { return cont(val);};};
auto style = [](const auto &val) { return val; };
auto mod = [](auto &&modv) { return [=](auto &&truecont){ return [=](auto &&falsecont) { return [=](auto &&val) { if (val % modv) { return truecont(val); } else { return falsecont(val); }; }; }; }; };
auto passing = [](auto &&val) { return [=](auto &&cont){ return [=](auto &&) {return cont(val);};};};

bool isLeapYear(int year){
  return (continuation)
    (year)
    ((continuation)
     (4)
     (mod)
     ((continuation)
      (false)
      (passing)
      (style)
      )
     ((continuation)
      (100)
      (mod)
      ((continuation)
       (true)
       (passing)
       (style))
      ((continuation)
       (400)
       (mod)
       ((continuation)
        (true)
        (passing)
        (style)
        )
       ((continuation)
        (false)
        (passing)
        (style)
        )
       )
      )
     );
}

int main() {
  std::vector<int> years{2019, 2020, 2021};
  for(auto year : years) {
    std::cout << year << (isLeapYear(year) ? " is " : " is not " ) << "a leap year\n";
  }
}

This is a submission to the 'is leap year' Bad Code challenge on Reddit: https://www.reddit.com/r/badcode/comments/cw5n21/bad_code_coding_challenge_18_is_leap_year/ezq904o/