Question

See my snippet below. I have a pretty good idea what the error is, but I wonder whether there is an easy way to query a PSQ using underscores when the key is a tuple. At least it looks very tempting :D.

main :: IO()
main = do
     time <- getCPUTime
     let qTuple = ("mine", 3455, msgs)
     let rrq = PSQ.singleton qTuple time
     let r = PSQ.lookup ("mine", _, _) rrq
     print (r)

Eventually I have messages destined for IPv4 addresses and TCP-Port numbers that need to be de-queued (after a while) in the order of their creation time: (IPv4, tport), (msg, ctime). On the one hand I want to be able to query if there is a queue for any given tuple (IPv4, tport) existing at all and either create such a queue if required or de-queue it a due-time.

Answer 1

If you’re asking whether you can use a syntax like that to look up any tuple that follows that form in a PSQ, the answer is no 🙂 It would be impossible to do that in general for all data structures, after all.

It sounds like you should allocate a unique identifier (is that what the number is?) to each item (stored in the item itself), and key the PSQ on that; then you could have Maps from the fields you care about indexing on (the string, the integer, or whatever) to the items; after that it’s just another lookup to get the priority. Of course, you’d need at the very least a Map from the unique identifiers to the items themselves.

(By the way, if these are the same tuples mentioned in your older question, I would suggest using a data type instead of a tuple.)