naive timer

naive_timer.hs

import Text.Parsec

type Parser = Parsec String ()

data T = T { hours :: Int, minutes :: Int, seconds :: Int }

instance Show T where
  show (T h m s) = show h ++ " hours " ++ show m ++ " minutes " ++ show s ++ " seconds"

parse' :: Parser a -> String -> Either ParseError a
parse' rule = parse rule "(source_file)"

timeP :: Char -> Parser Int
timeP c = option 0 $ try (valParser <* char c)

timeParser :: Parser T
timeParser = do
  h <- timeP 'h'
  m <- timeP 'm'
  s <- timeP 's'
  pure $ T h m s

valParser :: Parser Int
valParser = rd <$> many1 digit
  where rd = read :: String -> Int

toTime :: String -> T
toTime t = case parse' timeParser t of
  Left e -> error (show e)
  Right time' -> time'

-- Allows doing simple time parsing
-- toTime "1h23m1s" => 1 hour 23 minutes 1 second
-- allows skipping identifiers
-- toTime "22m20s" => 22 minutes 20 seconds