how to write a sum function with infinite number of arguments, using currying in javascript?

问题

I have tried writing the below code to find sum of 'n' numbers using sum function. I am getting the correct response in output. But i am unable to return that using sum function, as i always have to return a function, which is required for curried effect.

Please help. Thanks in advance.

var output = 0,
  chain;

function sum() {
  var args = Array.prototype.slice.call(arguments);
  output += args.reduce(function(a, b) {
    return a + b;
  });
  sumCurried = sum.bind(output);
  sumCurried.val = function() {
  return output;
  }
  return sumCurried;

}
debugger;
document.getElementById('demo').innerHTML = sum(1, 2)(3)(4);
// document.getElementById('demo').innerHTML = sum(1)(3)(4);

<p id='demo'></p>

enter code here

回答1:

You can add a stop condition to the curried function, for example - if the function is called without an argument return the output:

var output = 0,
  chain;

function sum() {
  var args = Array.prototype.slice.call(arguments);
  
  if(args.length === 0) {
    return output;
  }
  
  output += args.reduce(function(a, b) {
    return a + b;
  });
  sumCurried = sum.bind(output);
  
  return sumCurried;

}

console.log(sum(1, 2)(3)(4)());

<p id='demo'></p>

The returned curry function has a val property, which is a function that returns the current value:

var output = 0,
  chain;

function sum() {
  var args = Array.prototype.slice.call(arguments);
  output += args.reduce(function(a, b) {
    return a + b;
  });
  sumCurried = sum.bind(output);
  sumCurried.val = function() {
    return output;
  }
  return sumCurried;

}

console.log(sum(1, 2)(3)(4).val());

<p id='demo'></p>

回答2:

Why would you use currying at all? However, here is a shorter version:

 const sum = (...args) => {
   const func = (...s)=> sum(...args,...s);
   func.value = args.reduce((a,b)=>a+b,0);
   return func;
 };

 //usable as
sum(1,2).value,
sum(1,1)(1).value,
sum(1,1)(1,1)(1,1).value

And you always need to end the currying chain. However, it can be shortified:

  func.valueOf = ()=> args.reduce((a,b)=>a+b,0);
  //( instead of func.value = ... )

So when called you can do:

  +sum(1,2,3)
 +sum(1)(1)(1)

来源：https://stackoverflow.com/questions/46286531/how-to-write-a-sum-function-with-infinite-number-of-arguments-using-currying-in

标签

javascript

currying