simple run

run.js

function run(genfun) {
  var gen = genfun();
  
  function next(err, answer) {
    if (err) {
      return gen.throw(err);
    }
    
    var res = gen.next(answer);
    
    if (!res.done) {
      res.value(next);
    }
  }

  next();
}