[Haskell-beginners] data type

Alexander Chen alexander at chenjia.nl
Fri May 29 09:55:31 UTC 2020

import Data.Time

data DatabaseItem = DbString String
                  | DbNumber Integer
                  | DbDate   UTCTime
                  deriving  (Eq, Ord, Show)

theDatabase :: [DatabaseItem]
theDatabase =
    [ DbDate (UTCTime
             (fromGregorian 1911 5 1)
      (secondsToDiffTime 34250))
    , DbNumber 9001
    , DbString "Hello, world!"
    , DbDate (UTCTime
             (fromGregorian 1921 5 1)
             (secondsToDiffTime 34123))

My question:

I want to get the UTCTime.

So,  thisFunction :: [DatabaseItem] -> [UTCTime]

I don't need the answer but more the intuition (a link to a youtube etc. is also possible) how to handle these types of situations. Because i keep trying to think in terms of key:values (Python,Julia) which doesn't seem the right paradigm to approach this.

thanks in advance!

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