Documentation

A simple validation class using typeclass-metaprogramming (TMP) to help catch and generate Conduit-spec-abiding validation errors Intended for use on Aeson Parsers (in manual FromJSON instances) See also: NotBlank (example), (<!<), and (<?!<)

data IsRed = IsRed

instance Validation IsRed Text where
  validate = (== "red")
  errMsg = "must be red"

newtype Test = Test Text

instance FromJSON Test where
  parseJSON = withObject "Test" $ \v -> Test
    <$> v .: "test" <!< IsRed <!< NotBlank -- assurances are evaluated R->L

>>> eitherDecode @Test "{ \"test\": \"\" }"
Left "Error in $.test: can't be blank"

>>> eitherDecode @Test "{ \"test\": \"abc\" }"
Left "Error in $.test: must be red"

A property ensuing that the given json field isn't blank (intended for String/Text-like objects).

Represents errors as the spec describes.

Extracts and decodes an expected json body, intended for use with Validations. Returns the appropriate unprocessable errors the Conduit spec expects.

newtype Test = Test Text
  deriving (Show)

instance FromJSON Test where
  parseJSON = withObject "Test" $ \v -> Test
    <$> v .: "test" <!< NotBlank

endpoint = post "/" $ do
  result <- parseJsonBody @Test
  print text

Validates an optional json field *if it exists*.

Validates a json field.