Module

Data.Validation.Semigroup

Package: validation
Repository: purescript/purescript-validation

This module defines an applicative functor for applicative validation.

Applicative validation differs from monadic validation using Either in that it allows us to collect multiple errors using a Semigroup, whereas Either terminates on the first error.

#V Source

newtype V err result

The V functor, used for applicative validation

The Applicative instance collects multiple failures in an arbitrary Semigroup.

For example:

validate :: Person -> V (Array Error) Person
validate person = { first: _, last: _, email: _ }
  <$> validateName person.first
  <*> validateName person.last
  <*> validateEmail person.email

Constructors

V (Either err result)

Instances

Newtype (V err result) _
(Eq err, Eq result) => Eq (V err result)
(Eq err) => Eq1 (V err)
(Ord err, Ord result) => Ord (V err result)
(Ord err) => Ord1 (V err)
(Show err, Show result) => Show (V err result)
Functor (V err)
Bifunctor V
(Semigroup err) => Apply (V err)
(Semigroup err) => Applicative (V err)
(Semigroup err, Semigroup a) => Semigroup (V err a)
(Semigroup err, Monoid a) => Monoid (V err a)
Foldable (V err)
Traversable (V err)

#unV Source

unV :: forall r result err. (err -> r) -> (result -> r) -> V err result -> r

Unpack the V type constructor, providing functions to handle the error and success cases.

#invalid Source

invalid :: forall result err. err -> V err result

Fail with a validation error.

#isValid Source

isValid :: forall result err. V err result -> Boolean

Test whether validation was successful or not.

#toEither Source

toEither :: forall result err. V err result -> Either err result

#andThen Source

andThen :: forall b a err. V err a -> (a -> V err b) -> V err b

Apply a function if successful, to enable chaining of validation.

Similar to a monadic bind, except it is inconsistent with Apply - that is, where as apply accumulates failures: apply (invalid x) (invalid y) = invalid (x <> y), andThen has fail-fast semantics: andThen (invalid x) (\_ -> invalid y) = invalid x (>>= would be expected to be consistent).

Modules: Data.Validation.Semigroup; Data.Validation.Semiring