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36 lines
1.3 KiB
TeX
36 lines
1.3 KiB
TeX
\subsubsection{Haskell}
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\begin{examdetails}
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typically either short coding task or proof of program
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\end{examdetails}
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\paragraph{Programming}
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The best tip here is to read the Haskell book, and to solve the exercises during the semester.
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\subparagraph{Fold}
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One of the most important functions to understand is \texttt{foldr} (and \texttt{foldl}).
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If you have used \texttt{reduce} functions before, in e.g. JavaScript / TypeScript,
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they are similar to a \texttt{map} combined with a \texttt{reduce}.
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For instance, in TypeScript, the \texttt{reduce} function has the type signature
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\mint{typescript}|array.reduce( ( accumulator: A, current: A, idx: number, array: A[] ) => A, initialValue: A )|
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In the Haskell prelude, they are defined as follows:
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\begin{code}{haskell}
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foldr :: (a -> b -> b) -> b -> [a] -> b
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foldr f z [] = z
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foldr f z (x:xs) = f x (foldr f z xs)
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foldl :: (a -> b -> a) -> a -> [b] -> a
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foldl f z [] = z
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foldl f z (x:xs) = foldl f (f v x) xs
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\end{code}
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\subparagraph{zipWith}
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To combine a \texttt{map} and a \texttt{zip} function, use \texttt{zipWith}, type:
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\mint{haskell}|zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]|
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\TODO Add more remarks
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\paragraph{Proofs}
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These proofs use structural induction, see Section~\ref{sec:induction-proofs} for that.
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