branching.hs

import Data.Time

timeNow now =
  case todHour (localTimeOfDay (zonedTimeToLocalTime now)) < 12 of
    True  -> putStrLn "It's before noon"
    False -> putStrLn "It's after noon"

data ServicePlan = Free | Monthly | Annual

billAmount plan =
  case plan of
    Free    -> 0
    Monthly -> 5
    Annual  -> billAmount Monthly * 12

writeNumber i =
  case i of
    1 -> "one"
    2 -> "two"
    3 -> "three"
    _ -> "unknown number."

main =
  do
    now <- getZonedTime
    timeNow now

    let plan = Free
    putStrLn ("Customer owes " ++ show (billAmount plan)
              ++ " dollars.")

    let i = 2
    putStrLn ("Write " ++ show i ++ " as " ++ (writeNumber i))