tail-call-optimization

问题 So I recently came across case I needed to write code where callback calls itself and so on and wondered about NodeJS and tail-call support, so I found this answer https://stackoverflow.com/a/30369729 saying that yup, it's supported. So I tried it with this simple code: "use strict"; function fac(n){ if(n==1){ console.trace(); return 1; } return n*fac(n-1); } fac(5); Using Node 6.9.2 on Linux x64 and run it as node tailcall.js --harmony --harmony_tailcalls --use-strict and result was: Trace

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: Why doesn't .net/C# eliminate tail recursion? Take the following C# code: using System; namespace TailTest { class MainClass { public static void Main (string[] args) { Counter(0); } static void Counter(int i) { Console.WriteLine(i); if (i < int.MaxValue) Counter(++i); } } } The C# compiler (mine anyway) will compile the Counter method into the following CIL: .method private static hidebysig default void Counter

问题 Some VMs, most notably the JVM, are said to not support TCO. As a result, language like Clojure require the user to use loop recur instead. However, I can rewrite self-tail calls to use a loop. For example, here's a tail-call factorial: def factorial(x, accum): if x == 1: return accum else: return factorial(x - 1, accum * x) Here's a loop equivalent: def factorial(x, accum): while True: if x == 1: return accum else: x = x - 1 accum = accum * x This could be done by a compiler (and I've

问题 Supose you have a recursive function like: Blah.prototype.add = function(n) { this.total += n; this.children.forEach(function(child) { child.add(n); }); }; Is the child.add() a tail call? If not can it be written so it is? 回答1: Yes, it is a tail call: function(child) { child.add(n); // ^ tail } Yet nothing here is tail-recursive, because it's not a direct recursive call. Also this.children.forEach(…) is a tail call within the add method. However, the invocation of the callback within the

问题 So apparently, there's been a big brouhaha over whether or not Python needs tail call optimization. This came to a head when someone shipped Guido a copy of SICP because he didn't "get it." I'm in the same boat as Guido. I understand the concept of tail call optimization. I just can't think of any reason why Python really needs it. To make this easier for me to understand, could someone give me a snippet of code that would be greatly simplified using TCO? 回答1: Personally, i put great value on

问题 So apparently, there's been a big brouhaha over whether or not Python needs tail call optimization. This came to a head when someone shipped Guido a copy of SICP because he didn't "get it." I'm in the same boat as Guido. I understand the concept of tail call optimization. I just can't think of any reason why Python really needs it. To make this easier for me to understand, could someone give me a snippet of code that would be greatly simplified using TCO? 回答1: Personally, i put great value on

问题 In particular if I have the following code: func sum(n: Int, acc: Int) -> Int { if n == 0 { return acc } else { return sum(n - 1, acc + n) } } Will Swift compiler optimize it to a loop? And does it so in a more interesting case below? func isOdd(n: Int) -> Bool { if n == 0 { return false; } else { return isEven(n - 1) } } func isEven(n: Int) -> Bool { if n == 0 { return true } else { return isOdd(n - 1) } } 回答1: The best way to check is to examine the assembly language code generated by the

问题 Why won't the Scala compiler apply tail call optimization unless a method is final? For example, this: class C { @tailrec def fact(n: Int, result: Int): Int = if(n == 0) result else fact(n - 1, n * result) } results in error: could not optimize @tailrec annotated method: it is neither private nor final so can be overridden What exactly would go wrong if the compiler applied TCO in a case such as this? 回答1: Consider the following interaction with the REPL. First we define a class with a

问题 Is there a way to define a function in Clojure that is automatically tail-call-optimized? e.g. (defrecur fact [x] (if (= x 1) 1 (* x (fact (dec x))))) would be translated internally to something like: (defn fact [x] (loop [n x f 1] (if (= n 1) f (recur (dec n) (* f n))))) Can you tell me if something like this already exists? 回答1: The short answer is "No". The slightly longer answer is that Clojure is deliberately designed to require explicit indication where Tail Call Optimisation is desired

问题 According to answers to that question: Which, if any, C++ compilers do tail-recursion optimization? it seems, that compiler should do tail-recursion optimization. But I've tried proposed options and it seems that compiler can't do this optimization in case of template functions. Could it be fixed somehow? 回答1: I don't use the MS compilers, but GCC can certainly do tail-recursion optimisation for templates. Given this function: template <typename T> T f( T t ) { cout << t << endl; if ( t == 0