Minimal Haskell parsec example

data.txt

Sample1 [1100±30]
Sa2     [3200±50]
Sa3     [1400±20]
Sa4     [2000±30]
Sa6     [133413±70]
Sa7     [1300±30]
Sample9 [1300±50]
S8      [1600±30]

readData.hs

-- run with: cat data.txt | ./readData

import Prelude
import Control.Monad
import qualified Text.Parsec        as P
import qualified Text.Parsec.String as P
import qualified Text.Parsec.Number as P

data Sample = Sample String Age deriving (Show)
data Age = Age Integer Integer deriving (Show)

main :: IO ()
main = do 
  interact $ \s ->
    -- runParser :: ... -> Either ParseError a
    case P.runParser (P.sepEndBy sampleParser P.newline) () "" s of
      Left p  -> "Oh snap! \n" ++ show p
      Right x -> show x
  putStrLn ""

sampleParser :: P.Parser Sample
sampleParser = do
  id <- P.manyTill P.anyChar (P.string " ")
  _ <- P.manyTill (P.string " ") (P.string "[")
  mean <- read <$> P.many1 P.digit
  _ <- P.oneOf "±"
  std <- read <$> P.many1 P.digit
  _ <- P.oneOf "]"
  guard (mean >= 0 && mean <= 50000 ) P.<?> "valid age (between 50000 and 0)"
  return (Sample id (Age mean std))