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https://github.com/cdepillabout/focuslist
A Haskell data structure for lists with a focus
https://github.com/cdepillabout/focuslist
data-structure focus hacktoberfest haskell list
Last synced: 3 months ago
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A Haskell data structure for lists with a focus
- Host: GitHub
- URL: https://github.com/cdepillabout/focuslist
- Owner: cdepillabout
- License: bsd-3-clause
- Created: 2018-11-05T02:21:33.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2022-05-27T13:44:41.000Z (over 2 years ago)
- Last Synced: 2024-06-04T18:17:59.080Z (8 months ago)
- Topics: data-structure, focus, hacktoberfest, haskell, list
- Language: Haskell
- Homepage: http://hackage.haskell.org/package/focuslist
- Size: 75.2 KB
- Stars: 2
- Watchers: 5
- Forks: 3
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
Awesome Lists containing this project
README
FocusList
=========
[](http://travis-ci.org/cdepillabout/focuslist)
[](https://hackage.haskell.org/package/focuslist)
[](http://stackage.org/lts/package/focuslist)
[](http://stackage.org/nightly/package/focuslist)
[](./LICENSE)
A `FocusList` is a sequence of elements which has one element as its `Focus`. It
supports quick insertion and indexing by its implementation with
[`Seq`](http://hackage.haskell.org/package/containers-0.6.0.1/docs/Data-Sequence.html#t:Seq).
The focuslist package is similar to [pointed-list](http://hackage.haskell.org/package/pointedlist-0.6.1) or [list-zipper](http://hackage.haskell.org/package/ListZipper). Focuslist however is optimised for fast indexing and insertion at any point, and can be empty. For operations where linked lists perform better the other packages are likely to be superior, though for other operations focuslist is likely to be faster.
## Example
Here is a short example of using `FocusList`.
```haskell
module Main where
import Data.FocusList
( Focus(Focus), FocusList, appendFL, fromListFL, getFocusItemFL, prependFL
, singletonFL
)
import Data.Foldable (toList)
-- | Create a new 'FocusList' from a list. You must set the 'Focus' of the new
-- 'FocusList'. The 'Focus' is counting from zero, so the @goat@ element should
-- have the 'Focus'.
--
-- If you try to specify a 'Focus' out of range from the input list,
-- 'fromListFL' will return 'Nothing'.
myFocusList :: Maybe (FocusList String)
myFocusList = fromListFL (Focus 2) ["hello", "bye", "goat", "dog"]
-- | You can get the focused element from an existing 'FocusList'
--
-- If the 'FocusList' is empty, this returns 'Nothing'.
myFocusElement :: FocusList String -> Maybe String
myFocusElement focuslist = getFocusItemFL focuslist
-- | You can append to either side of a 'FocusList'.
--
-- 'singletonFL' creates a 'FocusList' with a single element.
-- That single element will have the 'Focus'.
--
-- 'myFocusListAppended' will have a value of
-- @FocusList (Focus 1) ["bye", "hello", "foobar"]@
myFocusListAppended :: FocusList String
myFocusListAppended =
prependFL "bye" (appendFL (singletonFL "hello") "foobar")
-- | 'FocusList' is an instance of 'Functor' and 'Foldable', so you can use
-- functions like 'fmap' and 'toList' on a 'FocusList'.
fmapAndConvertToList :: FocusList Int -> [String]
fmapAndConvertToList focuslist = toList (fmap show focuslist)
main :: IO ()
main = do
putStrLn "myFocusList:"
print myFocusList
putStrLn "\nmyFocusListAppended:"
print myFocusListAppended
putStrLn "\nmyFocusElement myFocusListAppended:"
print (myFocusElement myFocusListAppended)
putStrLn "\nfmap length myFocusListAppended:"
print (fmap length myFocusListAppended)
putStrLn "\nfmapAndConvertToList (fmap length myFocusListAppended):"
print (fmapAndConvertToList (fmap length myFocusListAppended))
```
## Maintainers
- [Grendel-Grendel-Grendel](https://github.com/Grendel-Grendel-Grendel)
- [cdepillabout](https://github.com/cdepillabout)