\begin{slide}{Generische Instanzen}

\begin{verbatim}
instance Show a => Show ( Maybe a ) where
    show m = case m of
        Nothing -> "Nothing"
        Just x  -> "Just" ++ show x
\end{verbatim}

das kann der Compiler selbst:
\begin{verbatim}
data Maybe a = ... 
    deriving ( Show )
\end{verbatim}

\end{slide}
