A core data type to realize references of mutable programing languages in Elm. After modifying target value by modify function, root value is also updated as an example bellow.

ref : Reference Int (List Int)
ref = fromRecord
    { this = 3
    , rootWith = \x -> [1,2] ++ x :: [4,5]
    }


this ref
--> 3


root ref
--> [ 1, 2, 3, 4, 5 ]


ref2 : Reference Int (List Int)
ref2 = modify (\n -> n + 1) ref


this ref2
--> 4


root ref2
--> [ 1, 2, 4, 4, 5 ]

Get focused object from Reference value.

ref : Reference Int (List Int)
ref = fromRecord
    { this = 2
    , rootWith = \x -> [1] ++ [x] ++ [3]
    }


this ref
--> 2

Pick out root object from Reference value.

ref : Reference Int (List Int)
ref = fromRecord
    { this = 2
    , rootWith = \x -> [1] ++ [x] ++ [3]
    }


root ref
--> [1, 2, 3]

Pick out root object from Reference value by specifying this value.

rootWith ref a == root <| modify (\_ -> a) ref

A constructor for Reference.

A constructor for Reference to create top root object.

ref : Reference (Maybe Int) (Maybe Int)
ref = top (Just 3)


this ref
--> Just 3


root ref
--> Just 3

Modify an object. It makes root object also changed.

ref : Reference Int (List Int)
ref = fromRecord
    { this = 2
    , rootWith = \x -> [1] ++ [x] ++ [3]
    }


modifiedRef : Reference Int (List Int)
modifiedRef = modify (\n -> n * 10) ref


this modifiedRef
--> 20


root modifiedRef
--> [1, 20, 3]

Change root object type by providing convert function.

ref : Reference Int (List Int)
ref = fromRecord
    { this = 4
    , rootWith = \x ->
        x :: [5]
    }


rootWith : List Int -> List (List Int)
rootWith ls =
    [[2, 3]] ++ [ls] ++ [[6, 7]]


newRef : Reference Int (List (List Int))
newRef = map rootWith ref


this ref
--> 4


root ref
--> [4, 5]


this newRef
--> 4


root newRef
--> [[2,3], [4,5], [6,7]]


modifiedRef : Reference Int (List (List Int))
modifiedRef = modify (\_ -> 8) newRef


this modifiedRef
--> 8


root modifiedRef
--> [[2,3], [8,5], [6,7]]