如何在scalaz-stream中实现wye.mergeLeftBiased

Question

我无法使用scalaz-stream实现以下功能：

echo '<script type="text/javascript">
    var select = document.getElementById("group_1");        
    var option = select.getElementsByTagName("option");
    for(j=0; j < option.length; j++){
        option[j].removeAttribute("selected");
    }
    option['.$i.'].setAttribute("selected","selected");
    select.onchange();

</script>';

我有一个尝试实现它的分支，但遗憾的是，即使在简单的情况下也是如此（如测试用例所示）。 scalaz-stream中/** * Same as `merge` but is biased on the left side. Both `merge` and `mergeLeftBias` are * non-deterministic, but `merge` tries to balance results from both to the extent the * input streams are producing results at roughly the same speed. `mergeLeftBias` * does not make any guarantees, but it will tend to grab elements from the left * before the right. This is can be useful if, for instance, working with two streams * that have interdependencies, i.e. the left stream produces results indirectly * from the right stream being pulled from. This is a fairly common scenario that * arises when using a `Queue` to merge "back" together a stream that was separated by * some black box API that was not build over scalaz-stream. */ def mergeLeftBias[I]: Wye[I,I,I] = ??? 的实现并不容易阅读（至少对我而言）。

https://github.com/jedesah/scalaz-stream/tree/topic/mergeLeftBiased