Enums, several different ways

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1

With reference to the discussion we had here:

How to do enums in Elm

I decided to have a go at creating an enums package for this. There is already one here:

https://package.elm-lang.org/packages/genthaler/elm-enum/latest/

One thing I found odd about that one was the signature for decoder:

decodeEnumValue : Enum a -> String -> Decoder a

Surely it should be:

decodeEnumValue : Enum a -> Decoder a

So the revised API I came up with is here, along with some examples of how to use it:

https://gist.github.com/rupertlssmith/2d24347a94efc68d1276d62363d00bbe

I left out the functions for creating HTML option or select, since those seem not to be a core concern of the data model.

Any thoughts?

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2

Also my package :wink:
https://package.elm-lang.org/packages/Herteby/enum/latest/

type Fruit
    = Apple
    | Banana
    | Mango

fruit : Enum Fruit
fruit =
    Enum.create
        [ ( "Apple", Apple )
        , ( "Banana", Banana )
        , ( "Mango", Mango )
        ]

type alias Enum a =
    { toString : a -> String
    , fromString : String -> Maybe a
    , encode : a -> Value
    , decoder : Decoder a
    , list : List ( String, a )
    }
3

Yes, saw that one too. Didn’t seem to be based on the “How to do enums in Elm” discussion though - but not completely dissimilar.

I think I could get Enum a -> a -> Int for free by having the make function enumerate the list of values, so would not need a separate model for EnumInt.

4

I think that requiring the pattern matcher (rather than listing) is better for the user, as it helps not forgetting stuff.
I’ve written about it in relation to elm-codec

5

What do you mean by ‘requiring the pattern matcher’? Can you give a little example in code, I don’t quite follow you.

6

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