Parsec example

metro.hs

import qualified Data.Text.IO as TIO
import Data.Maybe
import Data.Time
import Data.Time (defaultTimeLocale)

import Control.Monad
-- show
import Text.Parsec
import Control.Applicative

data Info = Info {
  hygrometry :: Float,
  temperature :: Float,
  pression :: Float,
  date :: LocalTime
  } deriving (Show)
-- A positive float with a comma instead of a dot
-- Assume there are always decimal !
posFloatC = rd <$> str
  where
    rd = read :: String -> Float
    str = do
      d1 <- number
      comma <- char ','
      d2 <- number
      return $ d1 ++ "." ++ d2

number = many1 digit
(<:>) a b = (:) <$> a <*> b
(<++>) a b = (++) <$> a <*> b

-- A positive float with a dot
-- Assume there are always decimal !
posFloat = rd <$> str
  where
    str = number <++> (char '.' <:> number)
    rd = read :: String -> Float


hygrometrieP = do
  string "Hygrométrie " *> spaces
  f <- posFloatC <* spaces
  char '%'
  return f

readHygrometry t = do
  let s = T.strip . head . filter (T.isInfixOf "Hygrométrie") . T.lines $ t
  parse hygrometrieP "readHygrometry" (T.unpack s)

temperatureP = do
  string "Température" *> spaces
  char ':' *> spaces
  f <- posFloatC
  spaces *> string "°C"
  return f

-- Température       :    21,0     °C      Pression atm.   : 1.013 hPa                                              Eau Ultrapure
readTemperature t = do
  let s = head . filter (T.isPrefixOf "Température") . T.lines $ t
  parse temperatureP "readTemperature" (T.unpack s)

pressionP = do
  string "Pression atm." *> spaces
  char ':' *> spaces
  f <- posFloat
  spaces *> string "hPa"
  return f

-- Température       :    21,0     °C      Pression atm.   : 1.013 hPa                                              Eau Ultrapure
readPressure t = do
  let s = head . filter (T.isInfixOf "Pression atm.") . T.lines $ t
  let s' = T.unpack . snd. T.breakOn "Pression atm" $ s
  parse pressionP "readPressure" s'

readDate :: Monad m => T.Text -> m LocalTime
readDate t = do
  let s = head . filter (T.isInfixOf "Opérateur") . T.lines $ t
  let s' = T.unpack . T.replace ": Le " "" . snd. T.breakOn ": Le " $ s
  return $ parseTimeOrError True defaultTimeLocale "%d/%m/%Y %H:%M:%S" s'

parserFloat p l = do
  case p l of
    Left e -> do
      putStrLn "Error parsing input:"
      print e
      return 99999
    Right r -> return r

main = do
  l <- TIO.readFile "metrologie.txt"
  p <- parserFloat readPressure l
  h <- parserFloat readHygrometry l
  t <- parserFloat readTemperature l
  d <- readDate l
  print $ Info h t p d