haskell learning project (ongoing) - manage a timesheet in the shell

main.hs (timesheetctl)

module Main (
            main
) where

-- | REF für Data Time https://two-wrongs.com/haskell-time-library-tutorial

import Data.Time
import System.Directory (doesFileExist)

data Status = Start | End | Break deriving Show

data Entry = Entry Status ZonedTime deriving Show

timeSheetEntry :: Status -> IO Entry -- can I make this pointfree
timeSheetEntry st = do
    nowHere <- getZonedTime
    return $ Entry st nowHere

storeEntry :: Entry -> IO ()
storeEntry (Entry s t) = do
    fileExist <- doesFileExist "./timesheet"
    case fileExist of
      True -> appendFile "timesheet" entry
      False -> writeFile "timesheet" firstentry
      where
        entry = show s ++ "," ++ show t ++ "\n"
        firstentry = "status,timestamp\n" ++ show s ++ "," ++ show t ++ "\n"

data Person = Person
    { status   :: !Status
    , timestamp :: ! -- Zoned time
    }

instance FromNamedRecord Person where
    parseNamedRecord r = Person <$> r .: "name" <*> r .: "salary"

loadCsv :: IO ()
main = do
    csvData <- BL.readFile "salaries.csv"
    case decodeByName csvData of
        Left err -> putStrLn err
        Right (_, v) -> V.forM_ v $ \ p ->
            putStrLn $ name p ++ " earns " ++ show (salary p) ++ " dollars"

main :: IO ()
main = do
    currentWorkDateTime <- timeSheetEntry Start
    putStrLn $ "Work Point: " ++ show currentWorkDateTime
    storeEntry currentWorkDateTime