What is the best practice in Haskell for defining constants in data properties?

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Take for example the code below..I've defined some shoes that are wearables with specific properties... (Nike, Adidas, Puma)

data Shoe = Nike | Adidas | Puma deriving Show

class Wearable a where
    forFeet :: a -> Bool
    forUpperBody :: a -> Bool
    comfortLevel :: a -> Int
    purchasePrice :: a -> Int
    from :: a -> String


instance Wearable Shoe where
    forFeet _ = True
    forUpperBody _ = False
    comfortLevel Nike = 5
    comfortLevel Adidas = 3
    comfortLevel Puma = 8
    purchasePrice Nike = 5
    purchasePrice Adidas = 3
    purchasePrice Puma = 3
    from _ = "The World Store"

Defining attributes such as purchasePrice, and comfortLevel on the different shoes within the instance of the typeclass feels a bit clunky here.. What is the best practice for this type of behavior in defining attributes of certain types?

haskell
1 Answers

I would say use a record instead of a class in this case:

data Shoe = Nike | Adidas | Puma deriving Show

data Wearable = Wearable
    { forFeet       :: Bool
    , forUpperBody  :: Bool
    , comfortLevel  :: Int
    , purchasePrice :: Int
    , from          :: String
    }

mkShoe :: Int -> Int -> Wearable
mkShoe comfort price = Wearable
    { forFeet       = True
    , forUpperBody  = False
    , comfortLevel  = comfort
    , purchasePrice = price
    , from          = "The World Store"
    }

nike, adidas, puma :: Wearable
nike   = mkShoe 5 5
adidas = mkShoe 3 3
puma   = mkShoe 8 3

getWearable :: Shoe -> Wearable
getWearable show = case shoe of
    Nike   -> nike
    Adidas -> adidas
    Puma   -> puma
user_152075680
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