Improve function composition slides

VL2.tex

@@ -376,7 +376,10 @@ Solution:
 (.) :: (b -> c) -> (a -> b) -> a -> c
 (.) f g x = f (g x)
 \end{haskellcode}
-\pause
+\end{frame}
+
+\begin{frame}[fragile]
+\frametitle{5. Function composition}
 And now you can chain functions together. Not just two! Look:
 \begin{haskellcode}
 f :: String -> Bool
@@ -385,6 +388,23 @@ f xs = (even . length . (\x -> x ++ "Hello world")) xs
 f xs = even . length . (\x -> x ++ "Hello world") $ xs
 \end{haskellcode}
 % $
+\pause
+Another example where currying is actually important:
+\begin{haskellcode}
+f :: Int -> Bool
+f x = even . (+) 3 . (-) 4 $ x
+
+-- why not this?
+f x = even . (+) 3 . (-) $ 4 x
+\end{haskellcode}
+%$
+\pause
+So there a few things that we have to be aware of:
+\begin{itemize}
+\item the types have to fit!
+\item the arity has to fit!
+\end{itemize}
+That sounds complicated at first, because it counts for the whole composition chain. But you'll get used to it.
 \end{frame}
 
 \section{6. Recursion patterns}