More class instances for Const.
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This commit uses `GeneralizedNewtypeDeriving` to simplify existing class
instance definitions for `Const`.
The approach used is similar to that used in `base`, which uses
`GeneralizedNewtypeDeriving` for `Semigroup` and `Monoid` (among others):
```hs
newtype Const a b = Const { getConst :: a }
deriving ( ...
, Semigroup -- ^ @SInCE base-4.9.0.0
, Monoid -- ^ @SInCE base-4.9.0.0
, ...
)
```
In practice, this mechanism generates method definitions that use
zero-cost coercions (see `Data.Coerce`).
This commit makes `Const` an instance of the following classes: - `DistributiveGCDMonoid` - `DistributiveLCMMonoid` - `Factorial` - `FactorialMonoid` - `GCDMonoid` - `LCMMonoid` - `LeftDistributiveGCDMonoid` - `LeftGCDMonoid` - `Monus` - `OverlappingGCDMonoid` - `RightDistributiveGCDMonoid` - `RightGCDMonoid` - `StableFactorial`
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This PR defines more class instances for the
Consttype.The approach used is similar to
base, which usesGeneralizedNewtypeDerivingto auto-derive instances ofSemigroupandMonoidforConst:(See source here.)
In addition, this PR:
GeneralizedNewtypeDerivingto simplify the remaining existing class instances forConst.Constclass instances.And finally:
Identityinstance forStableFactorial.(This was missing from More class instances for
Identity. #54)