Consider the following datatype
data Days
= Mon
| Tue
| Wed
| Thu
| Fri
| Sat
| Sun
deriving (Eq, Show, Data, Cyclic)
Cyclic provides ffw and rev functions that can be used to cycle trough the data constructors.
User needs to specify the number to use to calculate the resulting constructor and the starting constructor.
ghci > rev 2 Mon
Sun
ghci > ffw 33 Tue
Sun