Kombinatoren für Parser (I)

• Folge (and then) (ist bind aus der Monade)
• Auswahl (or)

  ( <|> ) :: Parser c a -> Parser c a -> Parser c a
  Parser f <|> Parser g = Parser $ \ s -> f s ++ g s
  

• beliebig viele

  many, many1 :: Parser c a -> Parser c [a]
  many p = many1 p <|> return [] 
  many1 p = do x <- p; xs <- many p; return $ x : xs
  

zahl :: Parser Char Integer = do 
   zs <- many1 ziffer 
   return $ foldl ( \ a z -> 10*a+z ) 0 zs