co + Generator 写的迭代器 类似 async.whilst

试着用用Koa，项目里原来有用到async 的whilst

用koa再用async感觉不太舒服，就用Generator+co写了个类似async whist的调用的主体功能，像传参这些没有作到

var co = require('co');

function* whilstGenerator(next, callback, end) {
        while (next) {
    yield callback()
        }
}

function whilst(test, callback, end) {
  var next = test()
  if (next) {
    co(whilstGenerator(next, function () {
      callback();
      whilst(test, callback)
    }))
  }
  end()
};

if (!module.parent) {
  var num = 0;
  whilst(function () { return num++ < 10 }, function () {
    console.log(num)
  }, function () {
    console.log("end")
  })
}
module.exports.whilst = whilst;