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Alex Rivera
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I tried to write a generalized maximum function similar to the one in Prelude . My first naiv approach looked like this: maximum' :: (F.Foldable a, Ord b) => a b -> Maybe b maximum' mempty = Nothing maximum' xs = Just $ F.foldl1 max xs However, when I test it it always returns Nothing regardless of the input: > maximum' [1,2,3] > Nothing Now I wonder whether it's possible to obtain the empty value of a Monoid type instance. A test function I wrote works correctly: getMempty :: (Monoid a) => a -> a getMempty _ = mempty > getMempty [1,2,3] > [] I had already a look at these two questions but I didn't figure out how the answers solve my problem: Write a Maximum Monoid using Maybe in Haskell Haskell Pattern Matching on the Empty Set How would I rewrite the maximum' function to get it to work ?
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