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Hello,
I defined an enumeration datatype like this
data MyType = One | Two | Four | Eight
and want to make it an instance of the class Enum. deriving Enum won't
do what I want, as it labels the items 0,1,2,3. Is there a better way to
do this than
instance Enum MyType where
fromEnum One = 1
fromEnum Two = 2
...
toEnum 8 = Eight
Something like
instance Enum MyType where
fromEnum One = 1
fromEnum x = 2*pred x
toEnum 1 = One
toEnum x = succ (toEnum x `div` 2)
Which doesn't work because succ and pred are not (properly?) defined. Is
there a way to let deriving Enum do *some* of work (i.e. defining succ
and pred) while manually defining the other functions?
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