関数プログラミングと無限論理多項式(39)

C# の例(15) (タプル)

Lisp への移植用にタプルを使って書き直しました。

    internal class Calc
    {
        private const int count = 21;
        private static IEnumerable<int> Take(int count, (Func<bool> next, Func<int> getCurrent, Action<int> setCurrent) iter)
        {
            for (int i = 0; i < count && iter.next(); i++)
            {
                yield return iter.getCurrent();
            }
        }
        private static IEnumerable<U> UnfoldL<T, U>(Func<T, (U, T)> next, T init)
        {
            (U dst, T src) = next(init);
            // 終了したとき next は src == null を返すとする
            if (src == null)
            {
                yield break;
            }
            yield return dst;
            // ここは foreach を使わないと書けない
            foreach (U e in UnfoldL(next, src))
            {
                yield return e;
            }
        }
        private static (int, (LongDecimal, LongDecimal, int)) GetNextDecimalDigitAndNumbers((LongDecimal, LongDecimal, int) numbers)
        {
            (LongDecimal number, LongDecimal square_difference, int scale) = numbers;
            (int, (LongDecimal, LongDecimal, int)) maxdd(int dd)
            {
                if (dd >= 0)
                {
                    LongDecimal two = new LongDecimal(2);
                    LongDecimal zd = new LongDecimal(dd).Shift(scale);
                    LongDecimal number_sq_diff = number * zd * two + zd * zd;
                    if (number_sq_diff <= square_difference)
                    {
                        return (dd, (number + zd, square_difference - number_sq_diff, scale + 1));
                    }
                    return maxdd(dd - 1);
                }
                return (0, (null, null, 0));
            }
            return maxdd(9);
        }
        private static (Func<bool> next, Func<int> getCurrent, Action<int> setCurrent) GenerateDecimal()
        {
            LongDecimal number = new LongDecimal();
            LongDecimal square_difference = new LongDecimal(3);
            (LongDecimal, LongDecimal, int) nums = (number, square_difference, 0);
            int current_digit = 0;
            bool next()
            {
                (current_digit, nums) = GetNextDecimalDigitAndNumbers(nums);
                return true;
            }
            int getCurrent()
            {
                return current_digit;
            }
            void setCurrent(int val)
            {
            }
            return (next, getCurrent, setCurrent);
        }
        public static string RepeatGenerator()
        {
            LongDecimal number = new LongDecimal();
            LongDecimal square_difference = new LongDecimal(3);
            (LongDecimal, LongDecimal, int) nums = (number, square_difference, 0);
            (Func<bool> next, Func<int> getCurrent, Action<int> setCurrent) generator = GenerateDecimal();
            int GetNextDecimalDigit()
            {
                generator.next();
                return generator.getCurrent();
            }
            LongDecimal repeat(LongDecimal number, int e, int count)
            {
                if (e < count)
                {
                    return repeat(number + new LongDecimal(GetNextDecimalDigit()).Shift(e), e + 1, count);
                }
                else
                {
                    return number;
                }
            }
            LongDecimal result_number = repeat(new LongDecimal(), 0, count);
            return result_number.Print();
        }
        public static string IterateGenerator()
        {
            return new LongDecimal(Take(count, GenerateDecimal())).Print();
        }
        public static string RepeatServer()
        {
            LongDecimal number = new LongDecimal();
            LongDecimal square_difference = new LongDecimal(3);
            (LongDecimal, LongDecimal, int) current_numbers = (number, square_difference, 0);
            LongDecimal repeat(LongDecimal number, int e, int count)
            {
                if (e < count)
                {
                    (LongDecimal, LongDecimal, int) numbers = current_numbers;
                    (int dd, (LongDecimal, LongDecimal, int) ns) = GetNextDecimalDigitAndNumbers(numbers);
                    current_numbers = ns;
                    return repeat(number + new LongDecimal(dd).Shift(e), e + 1, count);
                }
                else
                {
                    return number;
                }
            }
            LongDecimal result_number = repeat(new LongDecimal(), 0, count);
            return result_number.Print();
        }
        public static string IterateServer()
        {
            LongDecimal number = new LongDecimal();
            LongDecimal square_difference = new LongDecimal(3);
            (LongDecimal, LongDecimal, int) init_numbers = (number, square_difference, 0);
            return new LongDecimal(UnfoldL(GetNextDecimalDigitAndNumbers, init_numbers).Take(count)).Print();
        }
    }

Effective C# 6.0/7.0

Ｃ# 6 実践的プログラミング［入門］講座