javascript(函数式编程思考) ---> Map-Filter

let add = x=>x+1;
//Map :: (a -> b) -> [a] -> [b]
let Map = (function(result,f,arr){
    //闭包存储累积对象
    let result = [];
    return function map(f,arr){
            if(!Array.isArray(arr)){
                return "要处理的对象为数组";
            }
            if(arr.length ==0){
                return [];
            }else{
                let [head,...tail] = arr;
                result.push(f(head));
                // 通过回调map遍历目标对象arr,f处理过的元素存入result,tail为[]即遍历结束,可以返回result
                return tail.length == 0 ? result : map(f,tail);
            }
    }
})();
let test = Map(add,[1,2,3]);
console.log(test);//[2,3,4]

let biggerTen = x => x>10;
//Filter :: (a -> Bool) -> [a] -> [a]
let Filter = (function(){
    let result=[];
    return function filter(f,arr){
            if(!Array.isArray(arr)){
                return "要处理的对象为数组";
            }
            if(arr.length == 0){
                return [];
            }else{
                let [head,...tail] = arr;
                f(head) && result.push(head);
                return tail.length == 0 ? result : filter(f,tail);
            }
    };
})();

let testFilter = Filter(biggerTen,[1,5,10,44,12,2,5]);
console.log(testFilter);//[44,12]