dokondr wrote:
When I try to read POSIXTime... No instance for (Read POSIXTime)... What should I do to provide Read instance for POSIXTime?
Short answer: if you are thinking about this as a moment in time that could be parsed from the usual kind of string representation for that, you probably want to use UTCTime in your data type, not POSIXTime. If you really, really want to represent it internally as POSIXTime, then you should read those strings as UTCTime and then convert them to POSIXTime to store in your data type. I.e., in that case don't make your data type an instance of Read. POSIXTime is just a type alias for NominalDiffTime, i.e., a quantity of time between two moments. This is what the Show instance looks like: Prelude Data.Time> realToFrac 1000000 :: NominalDiffTime 1000000s By convention, the Read instance would expect a string in that format. Generally people aren't interested in that, so there is no Read instance. Even if you did want to parse that, you would just parse it as a number and then use realToFrac, as I did above. The rule of thumb is: always represent moments in time as a UTCTime. Regards, Yitz