使用golang和mgo，我如何在MongoDB中搜索一系列值？

我通过 mgo主页上的示例工作，但我正在努力寻找一种方法来查询值的范围。该行：

searchResults，searchErr = SearchReading（bson.M {k：key，t：{$ gte：start，$ lte：end}}，limit ）


失败：

line67：语法错误：意外的$

line67：复合字面值中缺少的类型

I worked through the example on the mgo homepage, but I'm struggling to find a way to query a range of values. The line:
searchResults, searchErr = SearchReading(bson.M{"k": key, "t": { $gte: start, $lte: end } }, limit)
fails with:
line67: syntax error: unexpected $
line67: missing type in composite literal

我忽略了非必要的代码位...

I left out the non-essential bits of code...

type Reading struct {
    K string  "k"
    T int64   "t"
    V float64 "v"
}

func SearchReading(q interface{}, limit int) (searchResults []Reading, searchErr string) {
    searchErr = ""
    searchResults = []Reading{}
    query := func(c *mgo.Collection) error {
        fn := c.Find(q).Limit(limit).All(&searchResults)
        if limit < 0 {
            fn = c.Find(q).All(&searchResults)
        }
        return fn
    }
    search := func() error {
        return withCollection("reading", query)
    }
    err := search()
    if err != nil {
        searchErr = "Database Error"
    }
    return
}

func GetReadingsForKey(key string, start int64, end int64, limit int) (searchResults []Reading, searchErr string) {
    searchResults, searchErr = SearchReading(bson.M{"k": key, "t": { $gte: start, $lte: end } }, limit)
    return
}