| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Cardano.CLI.Vary.Core
Documentation
data Vary (possibilities :: [Type]) Source #
Vary, contains one value out of a set of possibilities
Vary is what is known as a Variant type. This is also known as an open union or coproduct, among other names.
You can see it as the generalization of Either.
Conceptually, these are the same:
Vary [a, b, c, d, e] Either a (Either b (Either c (Either d e)))
However, compared to a deeply nested Either, Vary is:
- Much easier to work with;
- Much more efficient, as a single (strict) word is used for the tag.
Vary's can be constructed with Vary.from and values can be extracted using Vary.into and Vary.on .
Instances
| (Exception e, Exception (Vary errs), Typeable errs) => Exception (Vary (e ': errs)) Source # | See Vary and Exceptions for more info. |
Defined in Cardano.CLI.Vary.Core Methods toException :: Vary (e ': errs) -> SomeException Source # fromException :: SomeException -> Maybe (Vary (e ': errs)) Source # displayException :: Vary (e ': errs) -> String Source # | |
| (Typeable (Vary ('[] :: [Type])), Show (Vary ('[] :: [Type]))) => Exception (Vary ('[] :: [Type])) Source # | |
Defined in Cardano.CLI.Vary.Core Methods toException :: Vary ('[] :: [Type]) -> SomeException Source # fromException :: SomeException -> Maybe (Vary ('[] :: [Type])) Source # | |
| GenericHelper (a ': as) => Generic (Vary (a ': as)) Source # | Any non-empty Vary's generic representation is encoded similar to a tuple but with |
| Generic (Vary ('[] :: [Type])) Source # | Vary '[] 's generic representation is |
| (Typeable a, Show a, Show (Vary as)) => Show (Vary (a ': as)) Source # |
This allows us to print the name of the type which the current value is of.
|
| Show (Vary ('[] :: [Type])) Source # | |
| (NFData a, NFData (Vary as)) => NFData (Vary (a ': as)) Source # | |
Defined in Cardano.CLI.Vary.Core | |
| NFData (Vary ('[] :: [Type])) Source # | |
| (Eq a, Eq (Vary as)) => Eq (Vary (a ': as)) Source # | |
| Eq (Vary ('[] :: [Type])) Source # | |
| (Ord a, Ord (Vary as)) => Ord (Vary (a ': as)) Source # | |
Defined in Cardano.CLI.Vary.Core Methods compare :: Vary (a ': as) -> Vary (a ': as) -> Ordering Source # (<) :: Vary (a ': as) -> Vary (a ': as) -> Bool Source # (<=) :: Vary (a ': as) -> Vary (a ': as) -> Bool Source # (>) :: Vary (a ': as) -> Vary (a ': as) -> Bool Source # (>=) :: Vary (a ': as) -> Vary (a ': as) -> Bool Source # max :: Vary (a ': as) -> Vary (a ': as) -> Vary (a ': as) Source # min :: Vary (a ': as) -> Vary (a ': as) -> Vary (a ': as) Source # | |
| Ord (Vary ('[] :: [Type])) Source # | |
Defined in Cardano.CLI.Vary.Core Methods compare :: Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) -> Ordering Source # (<) :: Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) -> Bool Source # (<=) :: Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) -> Bool Source # (>) :: Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) -> Bool Source # (>=) :: Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) -> Bool Source # max :: Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) Source # min :: Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) -> Vary ('[] :: [Type]) Source # | |
| type Rep (Vary (a ': as)) Source # | |
Defined in Cardano.CLI.Vary.Core | |
| type Rep (Vary ('[] :: [Type])) Source # | |
Defined in Cardano.CLI.Vary.Core | |
pop :: forall a (as :: [Type]). Vary (a ': as) -> Either (Vary as) a Source #
Attempts to extract a value of the first type from the Vary.
If this failed, we know it has to be one of the other possibilities.
This function can also be seen as turning one layer of Vary into its isomorphic Either representation.
This function is not often useful in normal code, but super useful in generic code where you want to recurse on the variant's types.
For instance when implementing a typeclass for any Vary whose elements implement the typeclass:
instance Show (Vary '[]) where
show = Vary.exhaustiveCase
instance (Show a, Show (Vary as)) => Show (Vary (a : as)) where
show vary = case Vary.pop vary of
Right val -> "Vary.from " <> show val
Left other -> show otherTo go the other way: