lazy

gistfile1.txt

var noop = [];
function clone (arr){
    return arr.slice(0);
}
function stream(arr){
    if(arr.length === 0) return noop;
    return cons(function (){return arr[0]}, function (){ return stream(arr.slice(1))})
}

function cons(head, tail){
    return [head, tail];
}

function reduce(stream, fn, init){
    if(stream===noop) return init;
    else {
        return fn(function() {
            return reduce(stream[1](), fn, init)
        }, stream[0]())
    }
}
function map(stream, fn){
    return reduce(stream, function (a, v){
        return cons(function (){return fn(v)}, a);
    }, noop)
}

function filter(stream, fn){
    return reduce(stream, function (a, v){
        if(fn(v))return cons(function (){return v}, a);
        return a();
    }, noop)
}

function toArray(stream){
    var arr = [];
    reduce(stream, function(acc, v){
        arr.push(v)
        return acc();
    }, noop);
    return arr;
}

function take(stream, n){
    return reduce(stream, function(a, v){
        if(n <= 0) return noop;
        return cons(function(){return v}, function(){return take(a(),n-1)});
    }, noop)
}

function drop(stream, n){
    if(stream === noop) return noop;
    if(n>0) return drop(stream[1](),n-1);
    return stream;
}

function some(stream, fn){
    return reduce(stream, function(a,v){
        return fn(v) || a();
    }, false)
}

function all(stream, fn){
    return reduce(stream, function(a,v){
        return fn(v) && a();
    }, true)
}

c = filter(
    map(stream([1,2,3,4,5,6,7,8,9,10]),
        function(v){console.log('map:'+v);return v+1;}),
    function(v){console.log('filter:'+v);return v%2})
console.info(c[0]());
console.info(c[1]()[0]());
console.info(toArray(take(c,2)));
console.info(toArray(drop(c,2)));
console.info(all(c, function(v){return v<12}));
console.info(all(c, function(v){return v<6}));
console.info(some(c, function(v){return v>10}));
console.info(some(c, function(v){return v<0}));

어려워오. 주석주새오.

reduce 구현이 적절하지 않아보이네요. stream 은 기본 구현을 foldr (foldRight) 형태로 가져가야 합니다.
console.log(take(drop(num(0), 1000000), 1)) 같은 걸 해보면 reduce 구현때문에 스택오버플로가 납니다.
https://gist.github.com/jooyunghan/840ee284e9c1968063f7f48e87c692d5