如何从纯 JavaScript 函数恢复源代码？

Question

我所说的 Pure 是指在 λ 演算的意义上，即除了单参数函数和单参数函数调用之外，其主体上不包含任何内容的单参数函数。通过恢复源代码，我的意思是变量重命名。所以，例如，

n2 = function(v0){return function(v1){return v0(v0(v1))}}
console.log(source(n2));
console.log(source(n2(n2)));

应该打印：

function(v0){return function(v0){return v0(v0(v1))}}
function(v0){return function(v0){return v0(v0(v0(v0(v1))))}}

即第一行显示函数n2的原始源码，第二行显示n2(n2)求值返回的函数源码。

我已经设法实现如下：

function source(f){
    var nextVarId = 0;
    return (function recur(f){
        if (typeof f === "function"){
            if (f.isVarFunc) return f(null);
            else {
                var varName = "v"+(nextVarId++);
                var varFunc = function rec(res){
                    var varFunc = function(arg){
                        return arg === null
                            ? "("+res.join(")(")+")"
                            : rec(res.concat(recur(arg)));
                    };
                    varFunc.isVarFunc = true;
                    return varFunc;
                };
                varFunc.isVarFunc = true;
                var body = f(varFunc([varName]));
                body     = body.isVarFunc ? body(null) : recur(body);
                return "(function("+varName+"){return "+body+"})";
            };
        } else return f;
    })(f);
};

问题是我使用了一些相当丑陋的方法来标记函数，方法是将它们的名称设置为特定值，并且它在多次应用的函数中不起作用（例如 a(b)(b)).有没有更好的原则性方法来解决这个问题？

编辑：我设法设计了一个似乎在所有情况下都是正确的版本，但它仍然是一个丑陋的不可读的无原则的混乱。

Answer 1

最后，这是一个大大清理了上面的混乱的版本。

// source :: PureFunction -> String
// Evaluates a pure JavaScript function to normal form and returns the 
// source code of the resulting function as a string.
function source(fn){
    var nextVarId = 0;
    return (function normalize(fn){
        // This is responsible for collecting the argument list of a bound
        // variable. For example, in `function(x){return x(a)(b)(c)}`, it
        // collects `a`, `b`, `c` as the arguments of `x`.  For that, it
        // creates a variadic argumented function that is applied to many
        // arguments, collecting them in a closure, until it is applied to
        // `null`. When it is, it returns the JS source string for the
        // application of the collected argument list.
        function application(argList){
            var app = function(arg){
                return arg === null
                    ? "("+argList.join(")(")+")"
                    : application(argList.concat(normalize(arg)));
            };
            app.isApplication = true;
            return app;
        };
        // If we try to normalize an application, we apply
        // it to `null` to stop the argument-collecting.
        if (fn.isApplication) 
            return fn(null);
        // Otherwise, it is a JavaScript function. We need to create an
        // application for its variable, and call the function on it.
        // We then normalize the resulting body and return the JS
        // source for the function.
        else {
            var varName = "v"+(nextVarId++);
            var body    = normalize(fn(application([varName])));
            return "(function("+varName+"){return "+body+"})";
        };
    })(fn);
};

它仍然不完美，但看起来好多了。它按预期工作：

console.log(source(function(a){return function(b){return a(b)}}))

输出：

(function(v0){return (function(v1){return (v0)((v1))})})

虽然我想知道那是多么低效。

如何从纯 JavaScript 函数恢复源代码？

How can you recover the source code from a pure JavaScript function?

javascript

functional-programming

lambda-calculus