| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Data.Validation
Description
A data type similar to Data.Either that accumulates failures.
Synopsis
- data Validation err a
- validate :: Validate v => e -> (a -> Maybe b) -> a -> v e b
- validationNel :: Either e a -> Validation (NonEmpty e) a
- fromEither :: Either e a -> Validation e a
- liftError :: (b -> e) -> Either b a -> Validation e a
- validation :: (e -> c) -> (a -> c) -> Validation e a -> c
- toEither :: Validation e a -> Either e a
- orElse :: Validate v => v e a -> a -> a
- valueOr :: Validate v => (e -> a) -> v e a -> a
- ensure :: Validate v => e -> (a -> Maybe b) -> v e a -> v e b
- codiagonal :: Validation a a -> a
- validationed :: Validate v => (v e a -> v e' a') -> Validation e a -> Validation e' a'
- bindValidation :: Validation e a -> (a -> Validation e b) -> Validation e b
- _Failure :: Validate f => Prism (f e1 a) (f e2 a) e1 e2
- _Success :: Validate f => Prism (f e a) (f e b) a b
- class Validate f where
- _Validation :: Iso (f e a) (f g b) (Validation e a) (Validation g b)
- _Either :: Iso (f e a) (f g b) (Either e a) (Either g b)
- revalidate :: (Validate f, Validate g) => Iso (f e1 s) (f e2 t) (g e1 s) (g e2 t)
Data type
data Validation err a Source #
An Validation is either a value of the type err or a, similar to Either. However,
the Applicative instance for Validation accumulates errors using a Semigroup on err.
In contrast, the Applicative for Either returns only the first error.
A consequence of this is that Validation has no Bind or Monad instance. This is because
such an instance would violate the law that a Monad's ap must equal the
Applicative's <*>
An example of typical usage can be found here.
Instances
| Bifunctor Validation Source # | |
Defined in Data.Validation Methods bimap :: (a -> b) -> (c -> d) -> Validation a c -> Validation b d # first :: (a -> b) -> Validation a c -> Validation b c # second :: (b -> c) -> Validation a b -> Validation a c # | |
| Swap Validation Source # | |
Defined in Data.Validation Methods swap :: Validation a b -> Validation b a # | |
| Bitraversable Validation Source # | |
Defined in Data.Validation Methods bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Validation a b -> f (Validation c d) # | |
| Bifoldable Validation Source # | |
Defined in Data.Validation Methods bifold :: Monoid m => Validation m m -> m # bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> Validation a b -> m # bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> Validation a b -> c # bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> Validation a b -> c # | |
| Swapped Validation Source # | |
Defined in Data.Validation Methods swapped :: Iso (Validation a b) (Validation c d) (Validation b a) (Validation d c) # | |
| Validate Validation Source # | |
Defined in Data.Validation Methods _Validation :: Iso (Validation e a) (Validation g b) (Validation e a) (Validation g b) Source # _Either :: Iso (Validation e a) (Validation g b) (Either e a) (Either g b) Source # | |
| Functor (Validation err) Source # | |
Defined in Data.Validation Methods fmap :: (a -> b) -> Validation err a -> Validation err b # (<$) :: a -> Validation err b -> Validation err a # | |
| Semigroup err => Applicative (Validation err) Source # | |
Defined in Data.Validation Methods pure :: a -> Validation err a # (<*>) :: Validation err (a -> b) -> Validation err a -> Validation err b # liftA2 :: (a -> b -> c) -> Validation err a -> Validation err b -> Validation err c # (*>) :: Validation err a -> Validation err b -> Validation err b # (<*) :: Validation err a -> Validation err b -> Validation err a # | |
| Foldable (Validation err) Source # | |
Defined in Data.Validation Methods fold :: Monoid m => Validation err m -> m # foldMap :: Monoid m => (a -> m) -> Validation err a -> m # foldMap' :: Monoid m => (a -> m) -> Validation err a -> m # foldr :: (a -> b -> b) -> b -> Validation err a -> b # foldr' :: (a -> b -> b) -> b -> Validation err a -> b # foldl :: (b -> a -> b) -> b -> Validation err a -> b # foldl' :: (b -> a -> b) -> b -> Validation err a -> b # foldr1 :: (a -> a -> a) -> Validation err a -> a # foldl1 :: (a -> a -> a) -> Validation err a -> a # toList :: Validation err a -> [a] # null :: Validation err a -> Bool # length :: Validation err a -> Int # elem :: Eq a => a -> Validation err a -> Bool # maximum :: Ord a => Validation err a -> a # minimum :: Ord a => Validation err a -> a # sum :: Num a => Validation err a -> a # product :: Num a => Validation err a -> a # | |
| Traversable (Validation err) Source # | |
Defined in Data.Validation Methods traverse :: Applicative f => (a -> f b) -> Validation err a -> f (Validation err b) # sequenceA :: Applicative f => Validation err (f a) -> f (Validation err a) # mapM :: Monad m => (a -> m b) -> Validation err a -> m (Validation err b) # sequence :: Monad m => Validation err (m a) -> m (Validation err a) # | |
| Semigroup err => Apply (Validation err) Source # | |
Defined in Data.Validation Methods (<.>) :: Validation err (a -> b) -> Validation err a -> Validation err b # (.>) :: Validation err a -> Validation err b -> Validation err b # (<.) :: Validation err a -> Validation err b -> Validation err a # liftF2 :: (a -> b -> c) -> Validation err a -> Validation err b -> Validation err c # | |
| Alt (Validation err) Source # | For two errors, this instance reports only the last of them. |
Defined in Data.Validation Methods (<!>) :: Validation err a -> Validation err a -> Validation err a # some :: Applicative (Validation err) => Validation err a -> Validation err [a] # many :: Applicative (Validation err) => Validation err a -> Validation err [a] # | |
| (Eq err, Eq a) => Eq (Validation err a) Source # | |
Defined in Data.Validation Methods (==) :: Validation err a -> Validation err a -> Bool # (/=) :: Validation err a -> Validation err a -> Bool # | |
| (Data err, Data a) => Data (Validation err a) Source # | |
Defined in Data.Validation Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Validation err a -> c (Validation err a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Validation err a) # toConstr :: Validation err a -> Constr # dataTypeOf :: Validation err a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Validation err a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Validation err a)) # gmapT :: (forall b. Data b => b -> b) -> Validation err a -> Validation err a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Validation err a -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Validation err a -> r # gmapQ :: (forall d. Data d => d -> u) -> Validation err a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Validation err a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Validation err a -> m (Validation err a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Validation err a -> m (Validation err a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Validation err a -> m (Validation err a) # | |
| (Ord err, Ord a) => Ord (Validation err a) Source # | |
Defined in Data.Validation Methods compare :: Validation err a -> Validation err a -> Ordering # (<) :: Validation err a -> Validation err a -> Bool # (<=) :: Validation err a -> Validation err a -> Bool # (>) :: Validation err a -> Validation err a -> Bool # (>=) :: Validation err a -> Validation err a -> Bool # max :: Validation err a -> Validation err a -> Validation err a # min :: Validation err a -> Validation err a -> Validation err a # | |
| (Show err, Show a) => Show (Validation err a) Source # | |
Defined in Data.Validation Methods showsPrec :: Int -> Validation err a -> ShowS # show :: Validation err a -> String # showList :: [Validation err a] -> ShowS # | |
| Generic (Validation err a) Source # | |
Defined in Data.Validation Associated Types type Rep (Validation err a) :: Type -> Type # Methods from :: Validation err a -> Rep (Validation err a) x # to :: Rep (Validation err a) x -> Validation err a # | |
| Semigroup e => Semigroup (Validation e a) Source # | |
Defined in Data.Validation Methods (<>) :: Validation e a -> Validation e a -> Validation e a # sconcat :: NonEmpty (Validation e a) -> Validation e a # stimes :: Integral b => b -> Validation e a -> Validation e a # | |
| Monoid e => Monoid (Validation e a) Source # | |
Defined in Data.Validation Methods mempty :: Validation e a # mappend :: Validation e a -> Validation e a -> Validation e a # mconcat :: [Validation e a] -> Validation e a # | |
| (NFData e, NFData a) => NFData (Validation e a) Source # | |
Defined in Data.Validation Methods rnf :: Validation e a -> () # | |
| type Rep (Validation err a) Source # | |
Defined in Data.Validation type Rep (Validation err a) = D1 ('MetaData "Validation" "Data.Validation" "validation-1.1.1-inplace" 'False) (C1 ('MetaCons "Failure" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 err)) :+: C1 ('MetaCons "Success" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a))) | |
Constructing validations
validate :: Validate v => e -> (a -> Maybe b) -> a -> v e b Source #
validates an a producing an updated optional value, returning
e in the empty case.
This can be thought of as having the less general type:
validate :: e -> (a -> Maybe b) -> a -> Validation e b
validationNel :: Either e a -> Validation (NonEmpty e) a Source #
validationNel is liftError specialised to NonEmpty lists, since
they are a common semigroup to use.
fromEither :: Either e a -> Validation e a Source #
Converts from Either to Validation.
liftError :: (b -> e) -> Either b a -> Validation e a Source #
liftError is useful for converting an Either to an Validation
when the Left of the Either needs to be lifted into a Semigroup.
Functions on validations
validation :: (e -> c) -> (a -> c) -> Validation e a -> c Source #
validation is the catamorphism for Validation.
toEither :: Validation e a -> Either e a Source #
Converts from Validation to Either.
orElse :: Validate v => v e a -> a -> a Source #
v returns orElse aa when v is Failure, and the a in Success a.
This can be thought of as having the less general type:
orElse :: Validation e a -> a -> a
valueOr :: Validate v => (e -> a) -> v e a -> a Source #
Return the a or run the given function over the e.
This can be thought of as having the less general type:
valueOr :: (e -> a) -> Validation e a -> a
ensure :: Validate v => e -> (a -> Maybe b) -> v e a -> v e b Source #
ensure ensures that a validation remains unchanged upon failure,
updating a successful validation with an optional value that could fail
with e otherwise.
This can be thought of as having the less general type:
ensure :: e -> (a -> Maybe b) -> Validation e a -> Validation e b
codiagonal :: Validation a a -> a Source #
codiagonal gets the value out of either side.
validationed :: Validate v => (v e a -> v e' a') -> Validation e a -> Validation e' a' Source #
Run a function on anything with a Validate instance (usually Either) as if it were a function on Validation
This can be thought of as having the type
(Either e a -> Either e' a') -> Validation e a -> Validation e' a'
bindValidation :: Validation e a -> (a -> Validation e b) -> Validation e b Source #
bindValidation binds through an Validation, which is useful for
composing Validations sequentially. Note that despite having a bind
function of the correct type, Validation is not a monad.
The reason is, this bind does not accumulate errors, so it does not
agree with the Applicative instance.
There is nothing wrong with using this function, it just does not make a
valid Monad instance.
Prisms
These prisms are useful for writing code which is polymorphic in its choice of Either or Validation. This choice can then be made later by a user, depending on their needs.
An example of this style of usage can be found here
_Failure :: Validate f => Prism (f e1 a) (f e2 a) e1 e2 Source #
This prism generalises _Left. It targets the failure case of either Either or Validation.
_Success :: Validate f => Prism (f e a) (f e b) a b Source #
This prism generalises _Right. It targets the success case of either Either or Validation.
Isomorphisms
class Validate f where Source #
The Validate class carries around witnesses that the type f is isomorphic
to Validation, and hence isomorphic to Either.
Minimal complete definition
Methods
_Validation :: Iso (f e a) (f g b) (Validation e a) (Validation g b) Source #
_Either :: Iso (f e a) (f g b) (Either e a) (Either g b) Source #
Instances
| Validate Either Source # | |
Defined in Data.Validation | |
| Validate Validation Source # | |
Defined in Data.Validation Methods _Validation :: Iso (Validation e a) (Validation g b) (Validation e a) (Validation g b) Source # _Either :: Iso (Validation e a) (Validation g b) (Either e a) (Either g b) Source # | |
revalidate :: (Validate f, Validate g) => Iso (f e1 s) (f e2 t) (g e1 s) (g e2 t) Source #
revalidate converts between any two instances of Validate.