How can different types share data?

Question

type Animal
    = Dog DogData
    | Bird BirdData
    
type alias DogData =
    { name : String
    , runningSpeed : Float
    }
    
type alias BirdData =
    { name : String
    , wingSpan : Float
    }

{-| This function should work for all Animals
-}
getName {name} =
    name

Solution

type alias Animal =
    { name : String, data : AnimalData}

type AnimalData
    = Dog DogData
    | Bird BirdData
    
type alias DogData =
    { runningSpeed : Float
    }
    
type alias BirdData =
    { wingSpan : Float
    }

getName : Animal -> String
getName {name} =
    name

Alternative Solution

type Animal =
    Dog DogData
    | Bird BirdData

type alias AnimalData species =
    {species| name : String}
    
type alias DogData =
    AnimalData {runningSpeed:Float}

type alias BirdData =
    AnimalData {wingSpan:Float}

getName : AnimalData species -> String
getName {name} =
    name

Question

How can I write one function for all animals, that returns just the name.

Answer

Put the common data, in our case the name, all in one case and separate it from the differing data.

Further Reading

• 👥Thread: Passing accessors to functions