CODEWITHSUNDEEP
haskell
Anon Imous
Anon Imous

Reputation: 415

Haskell Container class

Is there a good standard (or just stable) implementation of (ordered) Container class?

Container class should provide basic manipulation operations with it's instances. Typical instances should be: Array, List, e.t.c.

Operations are:

Why do I need this? With the help of this class I can, for example, define some function for processing something in container, and use it with any container that I need.

Upvotes: 3

Views: 288

Answers (3)

misterbee
misterbee

Reputation: 5172

Data.Key.Indexed has several instances, including List, IntMap, and more

http://hackage.haskell.org/package/keys-0.2.2/docs/Data-Key.html#g:5

Upvotes: 2

raymonad
raymonad

Reputation: 949

It sounds like you may find ListLike interesting. index and take, respectively, cover the two operations you mentioned and it includes some 'typical instances'.

Upvotes: 3

daniel gratzer
daniel gratzer

Reputation: 53881

Kind of. This isn't Java so typeclass hierarchies are pretty rare. However, I think foldable is what you want

fold :: Monoid m => t m -> m
foldMap :: Monoid m => (a -> m) -> t a -> m
foldr :: (a -> b -> b) -> b -> t a -> b
foldl :: (b -> a -> b) -> b -> t a -> b

An example index function,

index i = snd . foldl' choose (0, Nothing)
  where choose (j, Just x) _  = (j, Just x)
        choose (j, Nothing) x | i == j    = (i, Just x)
                              | otherwise = (j + 1, Nothing)

Now using this you can trivially flatten any collection to a list and treat it as such, and there are more intelligent ways to fold over a collection and keep the ith entry.

To modify it, you could use traversable. It's another class with a few functions based around

traverse :: Applicative f => (a -> f b) -> t a -> f (t a)

Upvotes: 2

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