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Martin Hope
mali
Asked: 2025-01-13 19:20:34 +0800 CST
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Aqui estou tentando reimplementar um máximo seguro usando dobras

import Data.ByteString (foldl')

maximum' :: Ord a => [a] -> Maybe a
maximum'  = foldl  (\ acc x -> max acc (Just x)) Nothing

maximum'' :: Ord a => [a] -> Maybe a
maximum'' = foldl' (\ acc x -> max acc (Just x)) Nothing

A primeira função que usa foldl está funcionando corretamente, mas a segunda dá este erro:

• Couldn't match expected type ‘a’
              with actual type ‘GHC.Word.Word8’
  ‘a’ is a rigid type variable bound by
    the type signature for:
      maximum'' :: forall a. Ord a => [a] -> Maybe a
    at /home/mali/Projects/Deneme/HigherOrder.hs:60:1-36
• In the first argument of ‘Just’, namely ‘x’
  In the second argument of ‘max’, namely ‘(Just x)’
  In the expression: max acc (Just x)

Não deveria foldl'ser apenas uma versão mais eficiente de foldl?

haskell