Elm Enums

AsCustomType.elm

-- This way gives you a custom type, which can be used to branch on in code with case of.

type Pet
    = Cat
    | Dog
    | Snake
    | Spider


petEnum =
    Enum.make
        [ Cat
        , Dog
        , Snake
        , Spider
        ]
        (\pet ->
            case pet of
                Cat ->
                    "Cat"

                Doc ->
                    "Dog"

                Snake ->
                    "Snake"

                Spider ->
                    "Spider"
        )

AsGuardedType.elm

-- The Pet type could be made opaque so that outside of its defining module, new values cannot be added to the enum
-- The toString function is easy to write.
-- This enum is easy to modify, requiring only that a new item be added to the list.

type Pet
    = Pet String


petEnum =
    Enum.make
        [ Pet "Cat"
        , Pet "Dog"
        , Pet "Snake"
        , Pet "Spider"
        ]
        (\Pet kind -> kind)

AsListOfStrings.elm

-- This enum is just a string, so provides no guarantees that an instance of it really is in the enum.
-- The toString function is easy to write.
-- This enum is easy to modify, requiring only that a new item be added to the list.

petEnum =
    Enum.make
        [ "Cat"
        , "Dog"
        , "Snake"
        , "Spider"
        ]
        identity

Enum.elm

module Enum exposing (Enum, decoder, encoder, find, make)

type Enum a
    = Enum (List a) (a -> String)

make : List a -> (a -> String) -> Enum a

toString : Enum a -> a -> String

find : Enum a -> String -> Maybe a

decoder : Enum a -> Decoder a

encoder : Enum a -> a -> Value