Question at position 7 Given the following Haskell function: Which one of the following expressions correctly applies increment to a value of type Maybe Int? Clear my selection

Question

Question at position 7 Given the following Haskell function: Which one of the following expressions correctly applies increment to a value of type Maybe Int? Clear my selection

BlackTom AI · Accepted Answer

To determine which expression correctly applies increment to a Maybe Int, let’s examine the type and the available combinators. Option 1: fmap increment (Just 5) - Here, fmap has type (a -> b) -> t a -> t b, where t is a Functor. Maybe is a Functor, so fmap increment (Just 5) yields Just (increment 5), which is Just 6. This is valid and correctly applies the function inside the Maybe. Option 2: fold increment (Just 5) - There is no standard fold function with this type signature in the Prelude that would apply a single-argument function to a Maybe value in this way. This option is not well-typed for applying a function to a Maybe value. It conflates folding with direct mapping and doesn’t fit the typical API. Option 3: map increment (Just 5) - The function map has type (a -> b) -> [a] -> [b] in Prelude, i.e., it operates on lists. Just 5 is not a list, so this would fail to typecheck. This option is incorrect because map cannot be used with Maybe directly. Option 4: increment <*> (Just 5) - The (<*>) operator is for Applicative functors with type Maybe (a -> b) -> Maybe a -> Maybe b. To use it here, you’d need Just increment on the left, e.g., Just increment <*> Just 5. Since the left operand is plain increment (not wrapped in Maybe), this does not typecheck as written. This option misuses (<*>) for Maybe without wrapping the function.

Question at position 7 Given the following Haskell function: Which one of the following expressions correctly applies increment to a value of type Maybe Int? Clear my selection

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