edison question

I am quite confused with the collection package provided by the edison library. Attached is a sample program, what I wanted to do is to maintain a sorted of Pair of id and time (sorted by time). The error I got is: ghc -package data -package lang test.hs test.hs:17: No instance for `Collection.OrdColl c Pair' arising from use of `Collection.minElem' at test.hs:17 in a pattern binding: Collection.minElem sorted Actually I don't really understand what a class like "OrdColl c a" really means and how to use them. Please help! Regards, .paul.