Parsec + Haskell stuff

test.hs

module Main where                                                                                                                                                                              
                                                                                                                                                                                               
import Text.ParserCombinators.Parsec                                                                                                                                                           
    ( Parser                                                                                                                                                                                   
    , parse                                                                                                                                                                                    
    , string                                                                                                                                                                                   
    , try                                                                                                                                                                                      
    )                                                                                                                                                                                          
import Data.Foldable                                                                                                                                                                           
    ( asum                                                                                                                                                                                     
    )                                                                                                                                                                                          
                                                                                                                                                                                               
data Thing = Thing1                                                                                                                                                                            
           | Thing2                                                                                                                                                                            
           | Thing3                                                                                                                                                                            
             deriving (Show)                                                                                                                                                                   
                                                                                                                                                                                               
pairs :: [(String, Thing)]                                                                                                                                                                     
pairs = [ ("thing1", Thing1)                                                                                                                                                                   
        , ("thing2", Thing2)                                                                                                                                                                   
        , ("thing3", Thing3)                                                                                                                                                                   
        ]                                                                                                                                                                                      
                                                                                                                                                                                               
parseThing :: Parser Thing                                                                                                                                                                     
parseThing = asum parsers                                                                                                                                                                      
    where                                                                                                                                                                                      
      parsers = map mkParser pairs                                                                                                                                                             
                                                                                                                                                                                               
      mkParser (str, thing) =                                                                                                                                                                  
          try (string str >> return thing)                                                                                                                                                     
                                                                                                                                                                                               
main :: IO ()                                                                                                                                                                                  
main = do                                                                                                                                                                                      
  print $ parse parseThing "<stdin>" "thing1"                                                                                                                                                  
  print $ parse parseThing "<stdin>" "thing2"                                                                                                                                                  
  print $ parse parseThing "<stdin>" "thing3"                                                                                                                                                  
  print $ parse parseThing "<stdin>" "invalid input"