haskell-lectures/VL2/content/VL2_composition3.tex

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\ifger{Und jetzt können wir Funktionen verketten, egal wieviele:}{And now you can chain functions together. Not just two! Look:}
\begin{haskellcode}
f :: String -> Bool
f xs = (even . length . (\x -> x ++ "Hello world")) xs
-- or less ugly
f xs = even . length . (\x -> x ++ "Hello world") $ xs
\end{haskellcode}
% $
\pause
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\ifger{Ein anderes Beispiel, bei dem Currying tatsächlich relevant ist:}{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
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\ifger{Aber es gilt hier einige wichtige Dinge zu beachten:}{So there are a few things that we have to be aware of:}
\begin{itemize}
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\item \ifger{die Typen müssen passen!}{the types have to fit!}
\item \ifger{die Arität muss passen!}{the arity has to fit!}
\end{itemize}
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\ifger{Das klingt anfangs kompliziert, weil es für die gesamte Verkettung gilt, aber man kommt sehr schnell rein.}{That sounds complicated at first, because it counts for the whole composition chain. But you'll get used to it.}