Add pattern matching on MaybeInt

VL1.tex

@@ -520,6 +520,18 @@ calcSomething x
 \end{lstlisting}
 \end{frame}
 
+\begin{frame}[fragile]
+\frametitle{Algebraic Data Types (ctn.)}
+And pattern match on it as well:
+\setHaskellCodeStyle
+\begin{lstlisting}
+addIntToList :: MaybeInt -> [Int]
+addIntToList (NoError x) = [x]
+addIntToList (Error str) = []
+\end{lstlisting}
+So if we got an error, we just return an empty list, otherwise we return a list with the \code{Int} as its only element.
+\end{frame}
+
 \begin{frame}[fragile]
 \frametitle{Algebraic Data Types (ctn.)}
 Let's define something more complex. How about a tree?