javascript currying functions that return functions_javascript tips

The earliest curry function was a bit polymorphic, that is, branches were selected internally based on function parameters:

Copy code The code is as follows:

//http://www.openlaszlo.org/pipermail/laszlo-user/2005-March/000350.html
// ★★On 8 Mar 2005, at 00:06, Steve Albin wrote:

function add(a, b) {

if (arguments.length < 1) {

return add;

} else if (arguments.length < 2) {

return function(c) { return a c }

} else {

return a b;

}

}



var myadd = add( 2 );

var total = myadd(3);

A pioneer in Japan may have used very complex regularization and eval to come up with a function that is closer to the meaning of modern currying before he figured out that arguments can also be converted into arrays using Array's native method.

Copy code The code is as follows:

function curry(fun) {

if (typeof fun != 'function') {

throw new Error("The argument must be a function.");

}

if ( fun.arity == 0) {

throw new Error("The function must have more than one argument.");

}

var funText = fun.toString ();

var args = /function .*((.*))(.*)/.exec(funText)[1].split(', ');

var firstArg = args.shift();

var restArgs = args.join(', ');

var body = funText.replace(/function .*(.*) /, " ");

var curriedText =

"function (" firstArg ") {"

"return function (" restArgs ")" body

" }";

eval("var curried =" curriedText);

return curried;
}

function curry(fun) { if (typeof fun != 'function') { throw new Error("The argument must be a function."); } if (fun.arity == 0) { throw new Error("The function must have more than one argument."); } var funText = fun.toString(); var args = /function .*((.*))(.*)/.exec(funText)[1].split(', '); var firstArg = args.shift(); var restArgs = args.join(', '); var body = funText.replace(/function .*(.*) /, ""); var curriedText = "function (" firstArg ") {" "return function (" restArgs ")" body "}"; eval("var curried =" curriedText); return curried; } function sum(x, y) { return x y; } function mean3(a, b, c) { return (a b c)/3; } var a = curry(sum)(10)(15) alert(a)//25 var b = curry(mean3)(10)(20, 30); alert(b)//20 var c = curry(curry(sum))(10)()(20); alert(c); var d = curry(curry(mean3)(10))(20)(30); alert(d);
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Then the popularity of closures , and with the discovery of the technology of array conversion arguments, the modern currying function finally made its debut. Just like the geographical discovery of the Age of Discovery in the 15th to 17th centuries, the world of JavaScript suddenly opened up a lot.

Copy code The code is as follows:

//A simple modern currying function
function curry (fn, scope) {
var scope = scope || window;
var args = [];
for (var i=2, len = arguments.length; i < len; i) {
args.push(arguments[i]);
};
return function() {
fn.apply(scope, args);
};
}

General currying functions only have two functions. The execution situation is as follows. The first execution has insufficient parameters and returns to the internal function, and the second execution is finally completed. However, we can still do some articles regarding this parameter. Look at the following function:

Copy code The code is as follows:

function sum(){
var result=0;
for(var i=0, n=arguments.length; iresult = arguments[i];
}
return result;
}
alert(sum(1,2,3,4,5)); // 15

There is no so-called insufficient parameter problem. If you pass in a parameter, it will also calculate it. But what if no parameters are passed in? Correct, the difference is whether there are parameters or not. We can make it execute itself continuously if the parameters are present. Finally, it is executed once without parameters. In other words, the previous steps are used to store parameters.
var sum2= curry(sum);
sum2= sum2(1)(2)(3)(4)(5);
sum2(); // 15
Compared to the general Currying functions, this is a bit difficult. See the comments for details:

Copy code The code is as follows:

var curry= function(fn){ //The parameters of the original function are functions
return function(args){//The parameters of the internal function are arrays. Since they are executed immediately, they go directly to the third level
//args is relative to the third level internal The function can be a global variable
var self= arguments.callee;//Save itself (that is, the second function with the array as a parameter)
return function(){ //This is the second call Function
if(arguments.length){//If there are more parameters to be added
[].push.apply(args,arguments);//apply puts all the parameters currently passed in into args
return self(args);
}else{
return fn.apply(this,args);//The second parameter of apply is the array
}
}
}([ ]);
};

function sum(){ var result=0; for(var i=0, n=arguments.length; i<n i result="arguments[i];" return var curry="function(fn){//原函数的参数为函数" function self="arguments.callee;//把自身保存起来" if else fn.apply sum2="curry(sum);" alert><br><input onclick="runEx('runcode84050')" type="button" value="运行代码"> <input onclick="doCopy('runcode84050')" type="button" value="复制代码"> <input onclick="doSave(runcode84050)" type="button" value="保存代码">[Ctrl A Select all Note:<a href="http://www.jb51.net/article/23421.htm" title="查看具体详情" target="_blank">If you need to introduce external Js, you need to refresh to execute</a>]</n>

Or pass in multiple parameters each time:

function sum(){ var result=0; for(var i=0, n=arguments.length; i<n i result="arguments[i];" return var curry="function(fn){//原函数的参数为函数" function self="arguments.callee;//把自身保存起来" if else fn.apply sum2="curry(sum);" alert><br><input onclick="runEx('runcode62024')" type="button" value="运行代码"> <input onclick="doCopy('runcode62024')" type="button" value="复制代码"> <input onclick="doSave(runcode62024)" type="button" value="保存代码">[Ctrl A Select all Note:<a href="http://www.jb51.net/article/23421.htm" title="查看具体详情" target="_blank">If you need to introduce external Js, you need to refresh to execute</a>]</n>

But the above function has shortcomings. We need to put parentheses in the end. We want to return the result as long as the parameters are sufficient, and the extra parameters are ignored. The improvement is as follows:

<.>Copy code The code is as follows:

function curry(f) {
if (f.length == 0) return f;
function iterate(args) {
if (args.length <= f.length)
return f.apply(null, args);
return function () {
return iterate(args.concat(Array.prototype.slice.call(arguments)));
};
}
return iterate([]);
}

function curry(f) { if (f.length == 0) return f; function iterate(args) { if (args.length >= f.length) return f.apply(null, args); return function () { return iterate(args.concat(Array.prototype.slice.call(arguments))); }; } return iterate([]); } function mean3(a, b, c) { return (a b c) / 3; } var curriedMean3 = curry(mean3); alert(curriedMean3(1)(2, 3)); // => 2 alert(curriedMean3(1)(2)(3));//Empty brackets are invalid alert(curriedMean3()(1)()(2)()(3)); // => 2 alert(curriedMean3(1, 2)(3, 4)); // => 2 (the fourth parameter is invalid)
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