I'd like to make "Day" an instance of class "Enum," but the definition of
toEnum below seems to be completely wrong, because integers seem not permit
pattern matching. How is toEnum defined? Thanks.
data Day = Sunday | Monday
| Tuesday | Wednesday
| Thursday | Friday
| Saturday deriving (Eq, Ord, Show)
instance Enum Day where fromEnum Sunday = 0 fromEnum Monday
= 1 fromEnum Tuesday = 2 fromEnum Wednesday = 3 fromEnum
Thursday = 4 fromEnum Friday = 5 fromEnum Saturday =
6 toEnum 0 = Sunday toEnum 1 = Monday
toEnum 2 = Tuesday toEnum 3 = Wednesday
toEnum 4 = Thursday toEnum 5 = Friday
toEnum 6 = Saturday
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