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3v0k4/Main.purs

Last active December 21, 2019 00:17
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Revisions

  1. 3v0k4 revised this gist Dec 21, 2019. No changes.
  2. 3v0k4 created this gist Mar 18, 2019.
    47 changes: 47 additions & 0 deletions Main.purs
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,47 @@
    data Transaction
    = Deposit Info
    | Withdraw Info

    derive instance eqTransaction :: Eq Transaction

    instance showTransaction :: Show Transaction where
    show (Deposit i) = show i
    show (Withdraw i) = show i

    type Info =
    { timestamp :: DateTime
    , amount :: Int
    }

    deposit :: forall m. Monad m => m DateTime -> Int -> StateT (Array Transaction) m Unit
    deposit nowDateTime amount = do
    ts <- lift nowDateTime
    let t = Deposit { timestamp: ts, amount: amount }
    modify_ \ts -> ts <> [t]

    withdraw :: forall m. Monad m => m DateTime -> Int -> StateT (Array Transaction) m Unit
    withdraw nowDateTime amount = do
    ts <- lift nowDateTime
    let t = Withdraw { timestamp: ts, amount: amount }
    modify_ \ts -> ts <> [t]

    printStatement :: forall m. Monad m => (String -> m Unit) -> StateT (Array Transaction) m Unit
    printStatement logger = do
    s <- gets toStatement
    lift $ logger s

    toStatement :: Array Transaction -> String
    toStatement =
    fst <<< foldl fnc (Tuple "" 0)
    where
    fnc (Tuple s i) (Deposit d) =
    Tuple (s <> "\n" <> joinWith " " [ show d.timestamp, show d.amount, show $ i + d.amount]) (i + d.amount)
    fnc (Tuple s i) (Withdraw w) =
    Tuple (s <> "\n" <> joinWith " " [ show w.timestamp, "-" <> show w.amount, show $ i - w.amount]) (i - w.amount)

    main :: Effect Unit
    main = do
    flip evalStateT [] do
    deposit nowDateTime 500
    withdraw nowDateTime 100
    printStatement log