ZipperPull

This library makes it easier to attach interface as [linear zipper](https://en.wikipedia.org/wiki/Zipper_(data_structure)#Example:_Bidirectional_list_traversal "list zipper") on arbitrary data types including ordinary records. Actually, no data correction type is defined in this package: the only functions exposed here is create, which returns a record containing handler functions, not data itself, to treat your data like list zipper. So it is named ZipperPull, not Zipper itself.

INTERFACE TYPE

type alias ZipperPull stock model output =

{ next : model -> model

, prev : model -> model

, first : model -> model

, last : model -> model

, isFirst : model -> Bool

, isLast : model -> Bool

, foldFromFirst : (stock -> output -> output) -> output -> model -> output

, foldFromLast : (stock -> output -> output) -> output -> model -> output

, position : model -> Int

, toList : model -> List stock

}

A record containing functions for manipulating specified data type as list zipper.

CREATION

create :

{ getForeList : model -> List a

, getRearList : model -> List a

, getCurrent : model -> a

, setForeList : List a -> model -> model

, setRearList : List a -> model -> model

, setCurrent : a -> model -> model

}

-> ZipperPull a model b

The way you can attach list zipper interface on ordinary record (or any other data type).

type alias Model =
    { title : String
    , readCount : Int
    , previousVolumes : List (String, Int)
    , latterVolumes : List (String, Int)
    }


model : Model
model =
    { title = "Philosopher's Stone"
    , readCount = 3
    , previousVolumes = []
    , latterVolumes =
        [ ("Chamber of Secrets",2)
        , ("Prisoner of Azkaban",2)
        , ("Goblet of Fire",3)
        , ("Order of the Phoenix",2)
        , ("Half-Blood Prince",1)
        , ("Deathly Hallows",1)
        ]
    }


pull : ZipperPull (String, Int) Model output
pull =
    create
        { getForeList = .latterVolumes
        , getRearList = .previousVolumes
        , getCurrent = \m -> (m.title, m.readCount)
        , setForeList = \l m -> {m| latterVolumes = l}
        , setRearList = \f m -> {m| previousVolumes = f}
        , setCurrent = \(t,c) m -> {m| title=t, readCount=c}
        }


model
  |> pull.last
  |> pull.prev
  --> { title = "Half-Blood Prince" , readCount = 1 , previousVolumes = [ ("Order of the Phoenix", 2) , ("Goblet of Fire", 3) , ("Prisoner of Azkaban", 2) , ("Chamber of Secrets", 2) , ("Philosopher's Stone", 3) ] , latterVolumes = [ ("Deathly Hallows", 1) ] }


model |> pull.isFirst --> True


model |> pull.next |> pull.isFirst --> False


model |> pull.isLast --> False


model |> pull.last |> pull.isLast --> True


model
    |> pull.foldFromFirst
        (\(title, count) str ->
            str
            ++ "I have read \""
            ++ title
            ++ "\" "
            ++ String.fromInt count
            ++ " times. "
        )
        ""
        --> "I have read \"Philosopher's Stone\" 3 times. " ++ "I have read \"Chamber of Secrets\" 2 times. " ++ "I have read \"Prisoner of Azkaban\" 2 times. " ++ "I have read \"Goblet of Fire\" 3 times. " ++ "I have read \"Order of the Phoenix\" 2 times. " ++ "I have read \"Half-Blood Prince\" 1 times. " ++ "I have read \"Deathly Hallows\" 1 times. "


model
    |> pull.foldFromLast
        (\(_, count) sofar -> sofar + count)
        0
        --> 14


model
    |> pull.position
    --> 0

Modules

ZipperPull

kudzu-forest/elm-zipper-pull/1.0.1

ZipperPull

INTERFACE TYPE

CREATION

Modules