Using golang and mgo, how do I search for a range of values in MongoDB?

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` 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 } ```