Natural time in Haskell: `2 hours + 4 seconds`

time-natural.hs

{-# LANGUAGE FlexibleInstances, GeneralizedNewtypeDeriving #-}


newtype TimeUnit = TimeUnit Integer -- how many microseconds
  deriving (Eq, Show, Num)

instance Num (TimeUnit -> TimeUnit) where
  fromInteger n = \(TimeUnit scale) -> TimeUnit (n * scale)
  -- a + b = ... -- task for you

seconds, minutes, hours, days :: TimeUnit

seconds = TimeUnit 1000000
minutes = 60 seconds -- wow
hours   = 60 minutes -- such natural
days    = 24 hours


say :: String -> TimeUnit -> IO ()
say msg time = putStrLn $ "This is " ++ msg ++ show time

-- Examples
main = do
  say "3 minutes: " (3 minutes)
  say "100 days:  " (100 days )

  say "2 hours + 4 seconds: " (2 hours + 4 seconds)

Of course this also works if you would like your 3 minutes to be a plain Integer instead of a more type-safe TimeUnit:

{-# LANGUAGE FlexibleInstances #-}

instance Num (Integer -> Integer) where
  fromInteger n = \scale -> n * scale

seconds, minutes, hours, days :: Integer

seconds = 1000000 -- microseconds
minutes = 60 seconds -- wow
hours   = 60 minutes -- such natural
days    = 24 hours

say :: String -> Integer -> IO ()
say msg time = putStrLn $ "This is " ++ msg ++ show time

main = say "3 minutes: " (3 minutes)