var fusion = (function () {
    var min = Math.min;

    Iterator.prototype = {
        map: function (f) {
            return new MapIterator([f, this.at], this.length);
        },
        take: take,
        toArray: toArray
    };

    MapIterator.prototype = {
        map: function (f) {
            return new MapIterator([f].concat(this.fs), this.length);
        },
        take: take,
        toArray: toArray
    };

    return iterator;

    function compose(f, g) {
        return function (x) {
            return f(g(x));
        };
    }

    function iterator(a) {
        return new Iterator(function (index) {
            return a[index];
        }, a.length);
    }

    function Iterator(at, length) {
        this.at     = at;
        this.length = length;
    }

    function MapIterator(fs, length) {
        this.fs     = fs;
        this.at     = fs.reduce(compose);
        this.length = length;
    }

    function take(n) {
        return new Iterator(this.at, min(n, this.length));
    }

    function toArray() {
        var at     = this.at;
        var length = this.length;
        var array  = new Array(length);
        var index  = 0;

        while (index < length) array[index] = at(index++);

        return array;
    }
}());