The BoundedEnum thing is already something of a sunk cost, since there's
already magic behavior of Enum when a type is also Bounded. (Go look at how
Enum deriving is specified.)
On Fri, Jun 1, 2018 at 3:28 PM MarLinn
Counterargument: overlapping instances
instance (Bounded b, Enum b) => Enum (Either a b) instance (Bounded b) => Bounded (Either a b) instance (Applicative f, Bounded a) => Bounded (f a) instance (Bounded a, Enum a) => Enum (Either a b) instance (Bounded a) => Bounded (Either a b) instance (Bounded a, Enum a, Monoid b) => Enum (a, b) instance (Bounded b, Enum b, Monoid a) => Enum (a, b)
Also note that what you're talking about is a special type of objects, namely
type BoundedEnum a = (Bounded a, Enum a) -- using ConstraintKinds
(I'm sure the mathematicians have a better name for this)
So IF someone where to add these somewhere, might I suggest also adding essentials like
enumAll :: (Bounded a, Enum a) => [a] -- i.e. enumAll :: (BoundedEnum a) => [a]
Lastly, because it's its own type of objects, I'm sure there's a library out there doing just that. (Plus maybe other stuff like EnumMap's).
On 2018-06-01 20:32, Tom Ellis wrote:
True. I think I would propose
instance (Bounded a, Bounded b, Enum a, Enum b) => Enum (Either a b) instance (Bounded a, Bounded b) => Enum (Bounded a b) instance (Bounded a, Bounded b, Enum a, Enum b) => Enum (a, b)
On Fri, Jun 01, 2018 at 02:23:58PM -0400, Li-yao Xia wrote:
One issue is that (Int, Int) is too big to define toEnum/fromEnum.
On 06/01/2018 02:10 PM, Tom Ellis wrote:
I'm a bit surprised that whilst `Either` and `(,)` have instances for `Ord`
* `(,)` has no instance for `Enum` * `Either` has no instance for `Enum` or `Bounded`
Is there a particular reason for that? It might be tricky to implement
toEnum :: Int -> a fromEnum :: a -> Int
but in the presence of `Bounded` that should be possible.
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