CODEWITHSUNDEEP
haskellminimumfoldable
The Unfun Cat
The Unfun Cat

Reputation: 31918

How do I implement minimum with foldr (or foldMap)?

I want to implement minimum with foldr or foldMap. According to the exercise, it should have this definition:

mini :: (Foldable t, Ord a) => t a -> Maybe a -- named "mini" to avoid name clash

It sounded pretty straightforward, but I do not know what I can substiture for X below to make it work. Help please?

mini xs = Just (foldr min X xs)

And you get bonus points for showing me how to do it with foldMap too, but that seems harder.

Upvotes: 5

Views: 772

Answers (2)

Lee
Lee

Reputation: 144136

You could do:

mini :: (Foldable f, Ord a) => f a -> Maybe a
mini = foldr maybeMin Nothing
  where
    maybeMin x Nothing = Just x
    maybeMin x (Just y) = Just (min x y)

Upvotes: 5

iluetich
iluetich

Reputation: 1

You could try by replacing 'X' with the first element on the list. Of course you should now deal with the case when the function 'mini' gets invoked with an empty list.

Upvotes: -1

Related Questions