7.5 函数柯里化

add = function(){
    let sum = Array.from(arguments).reduce((a,b)=>{return a+b}, 0);
    let myAdd = function(){
        for(let i of Array.from(arguments)){
            sum+=i;
        }
        return myAdd
    }
    myAdd.valueOf = function(){
        return sum;
    }
    return myAdd
}