Relude.Extra.Enum

Mini bounded-enum framework inside relude.

Documentation

universe :: (Bounded a, Enum a) => [a]

Returns all values of some Bounded Enum in ascending order.

>>> data TrafficLight = Red | Blue | Green deriving (Show, Enum, Bounded)
>>> universe :: [TrafficLight]
[Red,Blue,Green]
>>> universe :: [Bool]
[False,True]

inverseMap :: forall a k. (Bounded a, Enum a, Ord k) => (a -> k) -> k -> Maybe a

inverseMap f creates a function that is the inverse of a given function f. It does so by constructing Map for every value f a. The implementation makes sure that the Map is constructed only once and then shared for every call.

The complexity of reversed mapping though is \(\mathcal{O}(\log n)\).

Usually you want to use inverseMap to inverse show function.

>>> data Color = Red | Green | Blue deriving (Show, Enum, Bounded)
>>> parse = inverseMap show :: String -> Maybe Color
>>> parse "Red"
Just Red
>>> parse "Black"
Nothing

next :: (Eq a, Bounded a, Enum a) => a -> a

Like succ, but doesn't fail on maxBound. Instead it returns minBound.

>>> next False
True
>>> next True
False
>>> succ True
*** Exception: Prelude.Enum.Bool.succ: bad argument

prec :: (Eq a, Bounded a, Enum a) => a -> a

Like pred, but doesn't fail on minBound. Instead it returns maxBound.

>>> prec False
True
>>> prec True
False
>>> pred False
*** Exception: Prelude.Enum.Bool.pred: bad argument

safeToEnum :: forall a. (Bounded a, Enum a) => Int -> Maybe a

Returns Nothing if given Int outside range.

>>> safeToEnum @Bool 0
Just False
>>> safeToEnum @Bool 1
Just True
>>> safeToEnum @Bool 2
Nothing
>>> safeToEnum @Bool (-1)
Nothing