5주차 Discussion

[chloe-codes1]

📢 책을 읽으면서 궁금한 점들을 자유롭게 적고 대답해주세요

5주차 진행 방식

1. 복습: 2.2 문제 풀어오기 - 17, 18, 20 - 27 (10문제)
2. 진도: 2.3까지 읽어오고 정리 & 의견 나누기
3. 미래 정하기: 2.3 에서 풀 문제 정하기

[bigsaigon333]

2.17

function last_pair(list) {
  return is_null(list) 
    ? null
    : length(list) === 1
    ? head(list)
    : last_pair(tail(list));
}

[bigsaigon333]

function last_pair(list) {
  return is_null(list) 
    ? null
    : is_null(tail(list))
    ? list(head(list))
    : last_pair(tail(list));
}

[sa02045]

const last_pair = (list) => (tail(list) === null ? list(head(list)) : last_pair(tail(list)));

[bigsaigon333]

#8 (comment)

[bigsaigon333]

2.18

function reverse(items) {
  return is_null(items)
    ? null
    : is_null(tail(items))
    ? head(items)
    : pair(
        reverse(tail(items)),
        pair(head(items), null),
      );
}

[sa02045]

function reverse(items){
    function reverse_iter(items, result){
        return is_null(items)
            ? result
            : reverse_iter(tail(items), pair(head(items), result));
    }
    return reverse_iter(items, []);
}

[iborymagic]

function reverse(items) {
  return length(items) === 2
    ? append(tail(items), head(items))
    : append(reverse(tail(items)), head(items));
}

[thgr8ganzi]

function reverse(list) {
    function reverseIter(list, reversed) {
        if (list === null) {
            return reversed;
        } else {
            const [x, y] = list;
            return reverseIter(y, pair(x, reversed));
        }
    }
    return reverseIter(list, null);
}
console.log(reverse(list(1, 4, 9, 16, 25)));

[bigsaigon333]

function reverse(list) {
    function reverseIter(list, reversed) {
        return reversed 
                  ? list === null
                  :  reverseIter(tail(list), pair(head(list), reversed));
    }
    return reverseIter(list, null);
}
console.log(reverse(list(1, 4, 9, 16, 25)));

[bigsaigon333]

2.20 (1)

function brooks(curried, list) {
  function iter(list) {
    return brooks(curried(head(list)), tail(list))
  }
  
  return is_null(list) ? curried : iter(list);
}

[bigsaigon333]

2.20 (2)

function brooks_curried(list) {
  return is_null(list)
    ? null
    : is_null(tail(list))
    ? head(list)
    : brooks_curried(
        pair(head(list)(head(tail(list)))),
        tail(tail(list)),
      );
}

[bigsaigon333]

2.21

function square_list(items) {
  return is_null(items)
    ? null
    : pair(head(items) ** 2, square_list(tail(items)));
}

function square_list(items) {
  return map(x => x ** 2, items)
}

[bigsaigon333]

2.23

function for_each(fun, items) {
  return is_null(items)
    ? null
    : (fun(head(items)), for_each(fun, tail(items)));
}

[sa02045]

function for_each(fn, items){
    if(is_null(items)){
        return true;
    } else {
        fn(head(items));
        return for_each(fn, tail(items));
    }
}

[bigsaigon333]

2.24

[1, [ [2, [ [3, [ 4, null ] ] ] ] ] ]

[sa02045]

https://mngu2382.github.io/sicp/chapter2/01-exercise07.html

[bigsaigon333]

2.25

// list(1, 3, list(5, 7), 9)
[
  1,
  [
    3,
    [
      [5, [7, null]],
      [9, null],
    ],
  ],
];

// list(list(7))
[[7, null], null];

// list(1, list(2, list(3, list(4, list(5, list(6, 7))))))
[
  1,
  [
    [
      2,
      [
        [
          3,
          [
            [
              4,
              [
                [
                  5,
                  [
                    [6, [7, null]],
                    null,
                  ],
                ],
                null,
              ],
            ],
            null,
          ],
        ],
        null,
      ],
    ],
    null,
  ],
];

[sa02045]

console.log((head(tail(head(tail(tail(list1)))))))
console.log(head(head(list2)));
console.log(head(tail(head(tail(head(tail(head(tail(head(tail(head(tail(list3)))))))))))))

[bigsaigon333]

2.26

// append(x, y)
[1, [2, [3, [4, [5, [6, null]]]]]];
list(1, 2, 3, 4, 5, 6);


// pair(x, y)
[
  [1, [2, [3, null]]],
  [4, [5, [6, null]]],
];
[list(1, 2, 3), list(4, 5, 6)];


// list(x, y)
[
  [1, [2, [3, null]]],
  [[4, [5, [6, null]]], null],
];
list(list(1, 2, 3), list(4, 5, 6));

[bigsaigon333]

// 2.27

// deep_reverse(x)
function deep_reverse(items) {
  return is_null(items)
    ? null
    : !is_pair(items)
    ? items
    : is_null(tail(items))
    ? deep_reverse(head(items))
    : pair(
        deep_reverse(tail(items)),
        pair(
          deep_reverse(head(items)),
          null,
        ),
      );
}

[sa02045]

function reverse(items) {
  function reverse_iter(items, result) {
    return is_null(items) ? result : reverse_iter(tail(items), pair(head(items), result));
  }

  return reverse_iter(items, null);
}

[chloe-codes1]

2.17

function lastPair(list) {
  return isNull(list) ? null : lastPair(tail(list) || head(list));
}

[iborymagic]

function last_pair(items) {
  return length(tail(items)) === 1
    ? list_ref(items, 1)
    : last_pair(tail(items));
}

[bigsaigon333]

list_ref(items, length(items)-1)