haskell-lectures/VL1/content/VL1_ADT4.tex

And now we can do sanity checks:
\begin{haskellcode}
calcSomething :: Int -> MaybeInt
calcSomething x
  | x < 100   = NoError (x * 5)
  | otherwise = Error "Int out of range!"
\end{haskellcode}
\pause
And pattern match on it as well:
\begin{haskellcode}
addIntToList :: MaybeInt -> [Int]
addIntToList (NoError x) = [x]
addIntToList (Error str) = []
\end{haskellcode}
So if we got an error, we just return an empty list, otherwise we return a list with the \hinline{Int} as its only element.