[Haskell-beginners] Abstracting Data.List

[mukesh tiwari]

Hi Giacomo,
Data.List can be abstracted using Foldable and Traversable but
unfortunately I could not find the functions corresponding to head, take.

Prelude Data.Traversable Data.Foldable> :t Data.Foldable.
Data.Foldable.Foldable    Data.Foldable.concatMap
Data.Foldable.foldl'      Data.Foldable.foldrM
Data.Foldable.minimum     Data.Foldable.sequenceA_
Data.Foldable.all         Data.Foldable.elem
Data.Foldable.foldl1      Data.Foldable.forM_
Data.Foldable.minimumBy   Data.Foldable.sequence_
Data.Foldable.and         Data.Foldable.find
Data.Foldable.foldlM      Data.Foldable.for_
Data.Foldable.msum        Data.Foldable.sum
Data.Foldable.any         Data.Foldable.fold
Data.Foldable.foldr       Data.Foldable.mapM_
Data.Foldable.notElem     Data.Foldable.toList
Data.Foldable.asum        Data.Foldable.foldMap
Data.Foldable.foldr'      Data.Foldable.maximum
Data.Foldable.or          Data.Foldable.traverse_
Data.Foldable.concat      Data.Foldable.foldl
Data.Foldable.foldr1      Data.Foldable.maximumBy   Data.Foldable.product
Prelude Data.Traversable Data.Foldable> :t Data.Traversable.
Data.Traversable.Traversable     Data.Traversable.for
Data.Traversable.mapAccumR       Data.Traversable.sequenceA
Data.Traversable.fmapDefault     Data.Traversable.forM
Data.Traversable.mapM            Data.Traversable.traverse
Data.Traversable.foldMapDefault  Data.Traversable.mapAccumL
Data.Traversable.sequence
Prelude Data.Traversable Data.Foldable> :i Foldable
class Foldable t where
  fold :: Data.Monoid.Monoid m => t m -> m
  foldMap :: Data.Monoid.Monoid m => (a -> m) -> t a -> m
  Data.Foldable.foldr :: (a -> b -> b) -> b -> t a -> b
  foldr' :: (a -> b -> b) -> b -> t a -> b
  Data.Foldable.foldl :: (a -> b -> a) -> a -> t b -> a
  foldl' :: (a -> b -> a) -> a -> t b -> a
  Data.Foldable.foldr1 :: (a -> a -> a) -> t a -> a
  Data.Foldable.foldl1 :: (a -> a -> a) -> t a -> a
      -- Defined in `Data.Foldable'
instance Foldable [] -- Defined in `Data.Foldable'
instance Foldable Maybe -- Defined in `Data.Foldable'
Prelude Data.Traversable Data.Foldable> :i Tr
Traversable  True
Prelude Data.Traversable Data.Foldable> :i Traversable
class (Functor t, Foldable t) => Traversable t where
  traverse ::
    Control.Applicative.Applicative f => (a -> f b) -> t a -> f (t b)
  sequenceA ::
    Control.Applicative.Applicative f => t (f a) -> f (t a)
  Data.Traversable.mapM :: Monad m => (a -> m b) -> t a -> m (t b)
  Data.Traversable.sequence :: Monad m => t (m a) -> m (t a)
      -- Defined in `Data.Traversable'
instance Traversable [] -- Defined in `Data.Traversable'
instance Traversable Maybe -- Defined in `Data.Traversable'
Prelude Data.Traversable Data.Foldable> :t foldMap
foldMap
  :: (Foldable t, Data.Monoid.Monoid m) => (a -> m) -> t a -> m

-Mukesh


On Fri, May 31, 2013 at 2:26 PM, Giacomo Tesio <giacomo at tesio.it> wrote:

> I'm looking for a class abstracting Data.List. I mean something that
> enable the use of say head, map, take and so on into different kind of
> types.
>
> Is there already something like that?
>
>
> Giacomo
>
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