DictAny k v and SetAny a

Modified versions of Dict and Set from elm/core. The keys can be any (non-function) type. A comparison function is used for every action that needs to compare keys.

• The comparison function is k -> k -> Order for DictAny k v
• and a -> a -> Order for SetAny a.

Usage

import SetAny as Set exposing (Set)


items : Set Item
items = [ Brush, Soap, Towel ] |> Set.fromList comparer


type Item
    = Brush
    | Soap
    | Shampoo
    | Towel


itemToInt : Item -> Int
itemToInt Item =
    case Item of
        Brush -> 1
        Soap -> 2
        Shampoo -> 3
        Towel -> 42


comparer : Item -> Item -> Order
comparer a b = compare (itemToInt a) (itemToInt b)


items |> Set.member comparer Shampoo --> False
items |> Set.member comparer Towel  --> True
items |> Set.toList --> [Towel, Soap, Brush]

Design Goals

• No functions stored in the model.
• No extra comparable type in the signatures.

Some other any key type implementations use a k -> comparable function, which requires the type signatures to include the comparable type, this is not necessary with this package.

Performance

The code is cloned from elm/core and the ordering function added. Performance depends on the complexity of the comparison function, but otherwise the same as the elm/core versions.

Downsides

The correct comparison function must be passed in every time, no compile time checking for this. If the Dict and Set code in elm/core is updated in the future, this package will also need to be updated to reflect the changes.

Implementation notes

I did try changing the internal names RBNode_elm_builtin and RBEmpty_elm_builtin, but the tests then failed. I found that these are magic values in the elm compiler, see here: github.com/elm/compiler.