IntervalMap usage example
In this example I use an IntervalMap to store a set of appointments. The appointments are for several people, so they can overlap.
This is a literate Haskell file, you can download it and compile it with ghc or run in in ghci. You must first install IntervalMap, if you have not already done so:
cabal install IntervalMap.
First I have to import the module:
> import Data.IntervalMap
For readability, here are simple type synonyms for our data types. In production code, one would of course use newtype or data for this.
> type Person = String > type Details = String
Again for readability, I use strings to represent timestamps. Also, to keep it shorter, I will omit the date and only use the time of the day in this example, e.g.: “09:00”, “12:47”.
> type Time = String > type TimeSpan = Interval Time
I have a time span include its start time but not its end time. So I use the IntervalCO constructor to get an interval that is closed at the startpoint but open at the endpoint:
> mkTimeSpan :: Time -> Time -> TimeSpan > mkTimeSpan from to = IntervalCO from to
An appointment consists of the timespan, the person, and the appointment details:
> type Appointment = (TimeSpan, Person, Details)
For a set of possible overlapping appointments, I store a list of (person, details) tuples for each timespan:
> type Appointments = IntervalMap Time [(Person, Details)]
Not that the key type is Time, not TimeSpan. That is, you specify the type of the endpoints, not the type of the interval itself.
Now I can define some helper functions.
A set containing no appointments:
> noAppointments :: Appointments > noAppointments = empty
To add an appointment to a set, I use (++) as a combining function to add the new appointment:
> addAppointment :: Person -> Time -> Time -> Details -> Appointments -> Appointments > addAppointment who from to what = insertWith (++) (mkTimeSpan from to) [(who, what)]
To look up all appointments at a given time, just get all entries containing that time:
> appointmentsAt :: Time -> Appointments -> [Appointment] > appointmentsAt t apps = [ (time, person, details) > | (time, pds) <- toAscList (apps `containing` t), > (person, details) <- pds ]
The function to get all appointments that overlap a given timespan is almost the same, just using intersecting instead:
> appointmentsDuring :: Time -> Time -> Appointments -> [Appointment] > appointmentsDuring from to apps = > [ (time, person, details) > | (time, pds) <- toAscList (apps `intersecting` mkTimeSpan from to), > (person, details) <- pds ]
Here is a sample set of appointments and a main function to show some test results:
> sampleApps :: Appointments > sampleApps = addAppointment "Paul" "09:00" "11:00" "Dentist" $ > addAppointment "John" "10:00" "11:30" "Meeting" $ > addAppointment "Rosy" "10:00" "11:30" "Shopping" $ > addAppointment "Lisa" "08:45" "09:15" "Bank" $ > noAppointments > > main :: IO () > main = do putStrLn (show (appointmentsAt "09:00" sampleApps)) > putStrLn (show (appointmentsDuring "09:30" "10:30" sampleApps))