instance Show haskell

Question

I got a data type "Cake"

*data Cake = EmptyBox | Food { name :: String
                                , flavors :: [Cake]} deriving( Read, Eq)*

instance Show Cake where
  show cake = prints cake where
   prints (Food name []) = name ++ "
"

I want to print cakes like this (each cake got different flavors)

Cake1
  Chocolate
  Nutella
    Strawberry
Cake2
  Chocolate
  Vanilla
Cake3

But I got error, doesn't works! How can I do it?

Answer 1

Since prints :: Cake -> String and flavors :: [Cake], we know

map prints flavors :: [String]

But this doesn't jive with the context in which it is used, since in

" " ++ expr

the " " is clearly a String and we therefore expect expr to be a String and not a [String].

To fix this, you should write or find a function which converts your [String] into a String in some way -- there are many candidate behaviors for this type, so you should decide what behavior you want and then find a way to achieve that behavior.