为什么C＃没有词法嵌套函数？

为什么C＃语言设计者可能没有包含对此类内容的支持（从计算机程序的结构和解释 ，第二版，第30页）：

/// 
Return the square root of x.
 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); } 

Answer 1

事实上，C＃就是这样。

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

Answer 2

就像Justice说的那样，你可以用C＃3.5和lambdas做到这一点; 如果你有C＃2.0，你可以使用匿名函数，虽然它会不那么性感：

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

编辑：我忘了，Func没有在C＃2.0中定义，所以你必须自己定义：

  public delegate TResult Func(T guess);