dlist-0.5: Differences listsContentsIndex
Data.DList
Portabilityportable (Haskell 98)
Stabilityexperimental
Maintainerdons@cse.unsw.edu.au
Contents
Construction
Basic functions
MonadPlus
Description
Difference lists: a data structure for O(1) append on lists.
Synopsis
newtype DList a = DL {
unDL :: [a] -> [a]
}
fromList :: [a] -> DList a
toList :: DList a -> [a]
empty :: DList a
singleton :: a -> DList a
cons :: a -> DList a -> DList a
snoc :: DList a -> a -> DList a
append :: DList a -> DList a -> DList a
concat :: [DList a] -> DList a
replicate :: Int -> a -> DList a
list :: b -> (a -> DList a -> b) -> DList a -> b
head :: DList a -> a
tail :: DList a -> DList a
unfoldr :: (b -> Maybe (a, b)) -> b -> DList a
foldr :: (a -> b -> b) -> b -> DList a -> b
map :: (a -> b) -> DList a -> DList b
maybeReturn :: MonadPlus m => Maybe a -> m a
Documentation
newtype DList a

A difference list is a function that given a list, returns the original contents of the difference list prepended at the given list

This structure supports O(1) append and snoc operations on lists, making it very useful for append-heavy uses, such as logging and pretty printing.

For example, using DList as the state type when printing a tree with the Writer monad 

 import Control.Monad.Writer
 import Data.DList
 
 data Tree a = Leaf a | Branch (Tree a) (Tree a)

 flatten_writer :: Tree x -> DList x
 flatten_writer = snd . runWriter . flatten
     where
       flatten (Leaf x)     = tell (singleton x)
       flatten (Branch x y) = flatten x >> flatten y
Constructors
DL
unDL :: [a] -> [a]
show/hide Instances
Construction
fromList :: [a] -> DList a
Converting a normal list to a dlist
toList :: DList a -> [a]
Converting a dlist back to a normal list
Basic functions
empty :: DList a
Create a difference list containing no elements
singleton :: a -> DList a
Create difference list with given single element
cons :: a -> DList a -> DList a
O(1), Prepend a single element to a difference list
snoc :: DList a -> a -> DList a
O(1), Append a single element at a difference list
append :: DList a -> DList a -> DList a
O(1), Appending difference lists
concat :: [DList a] -> DList a
O(spine), Concatenate difference lists
replicate :: Int -> a -> DList a
O(n), Create a difference list of the given number of elements
list :: b -> (a -> DList a -> b) -> DList a -> b
O(length dl), List elimination, head, tail.
head :: DList a -> a
Return the head of the list
tail :: DList a -> DList a
Return the tail of the list
unfoldr :: (b -> Maybe (a, b)) -> b -> DList a
Unfoldr for difference lists
foldr :: (a -> b -> b) -> b -> DList a -> b
Foldr over difference lists
map :: (a -> b) -> DList a -> DList b
Map over difference lists.
MonadPlus
maybeReturn :: MonadPlus m => Maybe a -> m a
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