Can I avoid repeated code when nesting two case statements in Elm?

user_42756 0
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I'm converting a Maybe String into a Date. I've type aliased Date as Birthdate for readability.

birthdate_from_url : Url.Url -> Birthdate
birthdate_from_url url =
    case url.query of
        Just query ->
            case Date.fromIsoString query of 
                Ok birthdate ->
                    birthdate

                Err _ ->
                    defaultBirthdate

        Nothing ->
            defaultBirthdate

With this nested case I'm having to call defaultBirthdate twice for each of the possible "failures".

Is there an alternative approach with or without the use of case?

elm case
1 Answers

You could use Maybe.map:

birthdate_from_url : Url.Url -> Birthdate
birthdate_from_url url =
    case url.query |> Maybe.map Date.fromIsoString of
        Just (Ok birthdate) ->
            birthdate

        _ ->
            defaultBirthdate
user_79435640
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