| Portability | portable |
|---|---|
| Stability | experimental |
| Maintainer | sjoerd@w3future.com |
Data.FMList
Contents
Description
FoldMap lists: lists represented by their foldMap function.
Examples:
-- A right-infinite list c = 1 `cons` c
-- A left-infinite list d = d `snoc` 2
-- A middle-infinite list ?? e = c `append` d
*> head e 1 *> last e 2
- newtype FMList a = FM {}
- transform :: (forall m. Monoid m => (a -> m) -> b -> m) -> FMList b -> FMList a
- empty :: Alternative f => forall a. f a
- singleton :: a -> FMList a
- cons :: a -> FMList a -> FMList a
- snoc :: FMList a -> a -> FMList a
- pair :: a -> a -> FMList a
- append :: FMList a -> FMList a -> FMList a
- fromList :: [a] -> FMList a
- fromFoldable :: Foldable f => f a -> FMList a
- null :: FMList a -> Bool
- length :: FMList a -> Int
- genericLength :: Num b => FMList a -> b
- head :: FMList a -> a
- tail :: FMList a -> FMList a
- last :: FMList a -> a
- init :: FMList a -> FMList a
- reverse :: FMList a -> FMList a
- toList :: Foldable t => t a -> [a]
- flatten :: Foldable t => FMList (t a) -> FMList a
- foldMapA :: (Foldable t, Applicative f, Monoid m) => (a -> f m) -> t a -> f m
- filter :: (a -> Bool) -> FMList a -> FMList a
- take :: (Ord n, Num n) => n -> FMList a -> FMList a
- drop :: (Ord n, Num n) => n -> FMList a -> FMList a
- takeWhile :: (a -> Bool) -> FMList a -> FMList a
- dropWhile :: (a -> Bool) -> FMList a -> FMList a
- zip :: FMList a -> FMList b -> FMList (a, b)
- zipWith :: (a -> b -> c) -> FMList a -> FMList b -> FMList c
- iterate :: (a -> a) -> a -> FMList a
- repeat :: a -> FMList a
- unfold :: (b -> FMList (Either b a)) -> b -> FMList a
- unfoldr :: (b -> Maybe (a, b)) -> b -> FMList a
Documentation
transform :: (forall m. Monoid m => (a -> m) -> b -> m) -> FMList b -> FMList aSource
The function transform transforms a list by changing
the map function that is passed to foldMap.
It has the following property:
transform a . transform b = transform (b . a)
For example:
m >>= g
= flatten (fmap g m)
= flatten . fmap g $ m
= transform foldMap . transform (. g) $ m
= transform ((. g) . foldMap) m
= transform (\f -> foldMap f . g) m
Construction
empty :: Alternative f => forall a. f a
The identity of <|>
fromFoldable :: Foldable f => f a -> FMList aSource
Basic functions
genericLength :: Num b => FMList a -> bSource
Folding
foldMapA :: (Foldable t, Applicative f, Monoid m) => (a -> f m) -> t a -> f mSource
Map each element of a structure to an action, evaluate these actions from left to right, and concat the monoid results.
Unfolding
unfold :: (b -> FMList (Either b a)) -> b -> FMList aSource
unfold builds a list from a seed value.
The function takes the seed and returns an FMList of values.
If the value is Right a, then a is appended to the result, and if the
value is Left b, then b is used as seed value in a recursive call.
A simple use of unfold (simulating unfoldl):
*> unfold (\b -> if b == 0 then empty else Left (b-1) `pair` Right b) 10 fromList [1,2,3,4,5,6,7,8,9,10]
unfoldr :: (b -> Maybe (a, b)) -> b -> FMList aSource
unfoldr builds an FMList from a seed value from left to right.
The function takes the element and returns Nothing
if it is done producing the list or returns Just (a,b), in which
case, a is a appended to the result and b is used as the next
seed value in a recursive call.
A simple use of unfoldr:
*> unfoldr (\b -> if b == 0 then Nothing else Just (b, b-1)) 10 fromList [10,9,8,7,6,5,4,3,2,1]