Text.JSON.FromJSValue

Interface for extracting data from JSValue.

Basic Parsing

class FromJSValue a where

Structures that can be parsed from JSON. Instances must declare either fromJSValue (parse directly from JSValue) or fromJSValueM (uses MonadReader)

Methods

fromJSValue :: JSValue -> Maybe a

fromJSValueM :: (JSValueContainer c, MonadReader c m) => m (Maybe a)

Instances

FromJSValue Bool

FromJSValue Double

FromJSValue Float

FromJSValue Int

FromJSValue Integer

FromJSValue String

FromJSValue ByteString

FromJSValue JSValue

FromJSValue a => FromJSValue [a]

FromJSValue a => FromJSValue (Maybe a)

Parsing any Maybe always returns Just

(FromJSValue a, FromJSValue b) => FromJSValue (a, b)

(FromJSValue a, FromJSValue b, FromJSValue c) => FromJSValue (a, b, c)

(FromJSValue a, FromJSValue b, FromJSValue c, FromJSValue d) => FromJSValue (a, b, c, d)

(FromJSValue a, FromJSValue b, FromJSValue c, FromJSValue d, FromJSValue e) => FromJSValue (a, b, c, d, e)

(FromJSValue a, FromJSValue b, FromJSValue c, FromJSValue d, FromJSValue e, FromJSValue f) => FromJSValue (a, b, c, d, e, f)

class FromJSValueWithUpdate a where

Structures that can be parsed from JSON if some structure for update is provided

Methods

fromJSValueWithUpdate :: Maybe a -> JSValue -> Maybe a

fromJSValueWithUpdateM :: (JSValueContainer c, MonadReader c m) => Maybe a -> m (Maybe a)

class MatchWithJSValue a where

Structures that can be matched with JSValue

Methods

matchesWithJSValue :: a -> JSValue -> Bool

matchesWithJSValueM :: (JSValueContainer c, MonadReader c m) => a -> m Bool

Data Extraction

jsValueField :: (JSValueContainer c, MonadReader c m, FromJSValue a) => String -> m (Maybe (Maybe a))

Reading the value that is on some field. Returns Nothing if JSON is not an object or field is present but cannot be parsed, 'Just Nothing' if absent, and 'Just (Just a)' otherwise

fromJSValueField :: (JSValueContainer c, MonadReader c m, FromJSValue a) => String -> m (Maybe a)

Reading the value that is on a field. Semantics are a bit involved, example GHCi session should clarify:

 Prelude> :set -XNoMonomorphismRestriction
 Prelude> let x = withJSValue (JSObject (toJSObject [(key,JSString $ toJSString value)]))
 Prelude> x (fromJSValueField key) :: IO (Maybe Int)
 Nothing
 Prelude> x (fromJSValueField key) :: IO (Maybe (Maybe Int))
 Just Nothing
 Prelude> x (fromJSValueField key) :: IO (Maybe (Maybe (Maybe Int)))
 Just (Just Nothing)
 Prelude> x (fromJSValueField key) :: IO (Maybe String)
 Just value
 Prelude> x (fromJSValueField key) :: IO (Maybe (Maybe String))
 Just (Just value)
 Prelude> x (fromJSValueField key) :: IO (Maybe (Maybe (Maybe String)))
 Just (Just (Just value))
 Prelude> let x = withJSValue (JSArray [])
 Prelude> x (fromJSValueField key) :: IO (Maybe String)
 Nothing
 Prelude> x (fromJSValueField key) :: IO (Maybe (Maybe String))
 Nothing
 Prelude> x (fromJSValueField key) :: IO (Maybe (Maybe (Maybe String)))
 Nothing

fromJSValueFieldBase64 :: (JSValueContainer c, MonadReader c m) => String -> m (Maybe ByteString)

Version of fromJSValueField for Base64 encoded data to avoid memory leak.

fromJSValueFieldCustom :: (JSValueContainer c, MonadReader c m) => String -> m (Maybe a) -> m (Maybe a)

Generalization of fromJSValueField. Does not use FromJSValue instances.

fromJSValueCustomMany :: (JSValueContainer c, MonadReader c m) => m (Maybe a) -> m (Maybe [a])

Runs parser on each element of underlaying json. Returns Just iff JSON is array.

fromJSValueCustomList :: (JSValueContainer c, MonadReader c m) => [m (Maybe a)] -> m (Maybe [a])

Generalization of fromJSValueCustomMany, where each element of array can have different parser.

fromJSValueManyWithUpdate :: (JSValueContainer c, MonadReader c m, FromJSValueWithUpdate a, MatchWithJSValue a) => [a] -> m (Maybe [a])

Runs parser on each element of underlying json. Returns Just iff JSON is an array.

Note: This method has quadratic complexity. It is better to write less general matching algorithms that use Maps.

Running

withJSValue :: Monad m => JSValue -> ReaderT JSValue m a -> m a

Simple runner