22 lines
811 B
TeX
22 lines
811 B
TeX
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But we can do more than enumerations. How about we do some error handling? Let's say we want a function to return an \code{Int}, but in case something went horribly wrong, we don't just want to return a 0 or some magic number, but a proper error message. Here we go:
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\pause
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\begin{haskellcode}
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data MaybeInt = NoError Int
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| Error String
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\end{haskellcode}
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\pause
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So constructors are just \emph{functions}! And they can have arguments, just like functions. Let's check their types:
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\begin{haskellcode}
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> :t NoError
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NoError :: Int -> MaybeInt
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> :t Error
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Error :: String -> MaybeInt
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\end{haskellcode}
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\pause
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And now we can do sanity checks:
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\begin{haskellcode}
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calcSomething :: Int -> MaybeInt
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calcSomething x
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| x < 100 = NoError (x * 5)
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| otherwise = Error "Int out of range!"
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\end{haskellcode}
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