Documentation

Datatype for checking if a validation holds for a subject.

• subject can be any data type for which assertions need to be checked.
• err can be any type representing an error, but it will only be possible to combine validators if the error type has a Semigroup instance.

Execute a validator by passing it to the validate function.

A Validator is both a Semigroup and a Monoid, making it possible to combine smaller validators into larger validators. A combined validator will accumulate errors from all of it's sub-validators.

Runs a validator on a subject.

The result is a Validation containing all accumulated errors, or the subject wrapped in a Success value.

Creates a validator that will return an error if the given predicate doesn't hold.

Since any predicate can be provided for checking if the subject satisfies certain conditions, this can be used to build your own custom validators.

Usage:

>>> let validator = assert (> 10) ["too small"]
>>> validate validator 11
Success 11

>>> validate validator 1
Failure ["too small"]

Creates a validator that will return an error if the given predicate holds.

Since any predicate can be provided for checking if the subject satisfies certain conditions, this can be used to build your own custom validators.

Usage:

>>> let validator = refute (> 10) ["too big"]
>>> validate validator 11
Failure ["too big"]

>>> validate validator 1
Success 1

Returns an error if a Maybe is Nothing.

Usage:

>>> let validator = ifNothing ["Found nothing."]
>>> validate validator Nothing
Failure ["Found nothing."]

>>> validate validator (Just "Bob")
Success (Just "Bob")

Returns an error if an Either contains a Left.

Usage:

>>> let validator = ifLeft ["Found left."]
>>> validate validator (Left 123)
Failure ["Found left."]

>>> validate validator (Right 456)
Success (Right 456)

Helper typeclass for checking if a value is empty.

Returns an error if the function returns an "empty" value.

Usage:

>>> let validator = ifEmpty ["Empty."]
>>> validate validator []
Failure ["Empty."]

>>> validate validator [1, 2, 3]
Success [1,2,3]
>>> validate validator (Map.fromList [('a', 1), ('b', 2)])
Success (fromList [('a',1),('b',2)])

Returns an error if the value has a size smaller than required.

Usage:

>>> let validator = minSize 3 ["Too small."]
>>> validate validator []
Failure ["Too small."]
>>> validate validator [1, 2]
Failure ["Too small."]

>>> validate validator [1, 2, 3]
Success [1,2,3]

Returns an error if the value has a size smaller than required.

Usage:

>>> let validator = maxSize 3 ["Too big."]
>>> validate validator [1, 2, 3, 4]
Failure ["Too big."]

>>> validate validator [1, 2, 3]
Success [1,2,3]

Helper typeclass for checking if a value contains only whitespace characters.

Returns an error if the function returns a value containing only whitespace.

Usage:

>>> let validator = ifBlank ["Only whitespace."]
>>> validate validator "   \t \n \r "
Failure ["Only whitespace."]

>>> validate validator "not empty"
Success "not empty"