In haskell we often use \textbf{pattern matching}. That means we define a function multiple times, but e.g. for different values of its input arguments. Let's see:
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\begin{haskellcode}
isZero :: Int -> Bool
isZero 0 = True
isZero x = False
\end{haskellcode}
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So if we pass it 0, we get True. If we do not pass 0, we get False and the value we passed gets basically ignored.
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What might happen if we remove the second or the third line? What is a \textbf{partial function} and a \textbf{total function}?