i am new to Haskell but i implemented this:

```
data Triple = T Double Double Double

instance Functor Triple where
    fmap f (T a b c) = T (f a) (f b) (f c)

```

then i tried to make the `Triple` a `Functor` but
i get this message:

```
**error:
    • Expected kind ‘* -> *’, but ‘Triple’ has kind ‘*’
    • In the first argument of ‘Functor’, namely ‘Triple’
      In the instance declaration for ‘Functor Triple**’

```

so my question is , do i really have to change the data Constructor to

```
data Triple a = a a a

```

???

this is my solution but is there a better one ?