为什么C#没有词汇嵌套函数? [英] Why doesn't C# have lexically nested functions?

问题描述

为什么C#语言设计人员可能不包括对类似内容的支持(源自计算机程序的结构和解释，第二版，第30页):

Why might the C# language designers not have included support for something like this (ported from Structure and Interpretation of Computer Programs, second ed., p. 30):

/// <summary>Return the square root of x.</summary>
double sqrt(double x) {
  bool goodEnough(double guess) {
    return Math.Abs(square(guess) - x) < 0.001;
  }
  double improve(double guess) {
    return average(guess, x / guess);
  }
  double sqrtIter(double guess) {
    return goodEnough(guess) ? guess : sqrtIter(improve(guess));
  }
  sqrtIter(1.0);
}

推荐答案

事实上，C#确实有这个.

In fact, C# has exactly this.

double sqrt(double x) {
    var goodEnough = new Func<double, bool>(guess =>
        Math.Abs(square(guess) - x) < 0.001
    );
    var improve = new Func<double, double>(guess =>
        average(guess, x / guess)
    );
    var sqrtIter = default(Func<double, double>);
    sqrtIter = new Func<double, double>(guess =>
        goodEnough(guess) ? guess : sqrtIter(improve(guess))
    );
    return sqrtIter(1.0);
}

这篇关于为什么C#没有词汇嵌套函数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！