Question: I have a snippet of code in which I have declared two datatypes. I've auto-derived both as members of the typeclass `enum`, however, I dislike that they are not "circular". By this, I mean that calling `succ Sun` should yield me `Mon`. `succ Dec` should result in `Jan`. So instead of writing my own enum I did this:

```
data WeekDay = Mon | Tue | Wed | Thu | Fri | Sat | Sun
             deriving (Enum, Show, Eq, Bounded)

data Month = Jan | Feb | Mar | Apr | May | Jun | July | Aug | Sep | Oct | Nov 
             | Dec
           deriving (Enum, Show, Eq, Bounded)

class Circ a where
  next :: Enum a => a -> a

instance Circ WeekDay where
  next a = if a == maxBound then minBound else succ a

instance Circ Month where      -- this is nearly identical to the one above
  next a = if a == maxBound then minBound else succ a

```

My question is: Is there a neater, less redundant way of writing this? In other words, I have two nearly identical instances written, with the datatype name (WeekDay vs. Month) being the only variable that changed.

Answer: 
```
class (Enum a, Bounded a, Eq a) => Circ a where
     next :: a -> a
     next a = if a == maxBound then minBound else succ a

instance Circ WeekDay
instance Circ Month

```
You could add `prev` too 

```
class (Enum a, Bounded a, Eq a) => Circ a where
     next :: a -> a
     next a = if a == maxBound then minBound else succ a
     prev :: a -> a
     prev a = if a == minBound then maxBound else pred a

```