Kapitel 1: Haskell in einer Nußschale

hugs Hello
ghc Hello.lhs

> import Prelude hiding ( putStrLn, getLine )

> putStrLn                      :: String -> IO ()
> putStrLn []                   =  putChar '\n'
> putStrLn (c : s)              =  putChar c >> putStrLn s

> getLine                       :: IO String
> getLine                       =  getChar >>= \ c ->
>                                  if c == '\n' then
>                                      return ""
>                                  else
>                                      getLine >>= \ s ->
>                                      return (c : s)

> getLine'                      :: IO String
> getLine'                      =  do c <- getChar
>                                     if c=='\n' then return ""
>                                                else do s <- getLine'
>                                                        return (c : s)

> main				:: IO ()
> main                          =  putStrLn "hello world"

Testausdrücke:

getLine >>= putStrLn
putStr "Eingabe: " >> getLine >>= \ line -> putStrLn ("Ausgabe: " ++ line)