Safe Haskell	Safe-Inferred
Language	Haskell2010

Data.Aeson.Possible

Description

Three-valued possible types for use with aeson.

Useful for use in PATCH endpoints: use in records which have ToJSON and FromJSON instances.

See the README for suggested usage.

The Alternative instance can be used to update a record (with PATCH data) as the LHS data is kept unless it is missing:

-- PATCH uses new data
HaveData new <|> old == HaveData new

-- PATCH sets null
HaveNull <|> old == HaveNull

-- PATCH did not change data
Missing <|> old == old

Documentation

data Possible a Source #

Constructors

Missing
HaveNull
HaveData a

Instances

Instances details

Alternative Possible Source #	Similar to the `Alternative Maybe` instance, picks the leftmost `HaveData` value.
Instance details Defined in Data.Aeson.Possible Methods empty :: Possible a # (<\|>) :: Possible a -> Possible a -> Possible a # some :: Possible a -> Possible [a] # many :: Possible a -> Possible [a] #
Applicative Possible Source #
Instance details Defined in Data.Aeson.Possible Methods pure :: a -> Possible a # (<>) :: Possible (a -> b) -> Possible a -> Possible b # liftA2 :: (a -> b -> c) -> Possible a -> Possible b -> Possible c # (>) :: Possible a -> Possible b -> Possible b # (<*) :: Possible a -> Possible b -> Possible a #
Functor Possible Source #
Instance details Defined in Data.Aeson.Possible Methods fmap :: (a -> b) -> Possible a -> Possible b # (<$) :: a -> Possible b -> Possible a #
Generic (Possible a) Source #
Instance details Defined in Data.Aeson.Possible Associated Types type Rep (Possible a) :: Type -> Type # Methods from :: Possible a -> Rep (Possible a) x # to :: Rep (Possible a) x -> Possible a #
Show a => Show (Possible a) Source #
Instance details Defined in Data.Aeson.Possible Methods showsPrec :: Int -> Possible a -> ShowS # show :: Possible a -> String # showList :: [Possible a] -> ShowS #
Eq a => Eq (Possible a) Source #
Instance details Defined in Data.Aeson.Possible Methods (==) :: Possible a -> Possible a -> Bool # (/=) :: Possible a -> Possible a -> Bool #
FromJSON a => FromJSON (Possible a) Source #	Uses `omittedField` to default to `Missing`
Instance details Defined in Data.Aeson.Possible Methods parseJSON :: Value -> Parser (Possible a) # parseJSONList :: Value -> Parser [Possible a] # omittedField :: Maybe (Possible a) #
ToJSON a => ToJSON (Possible a) Source #	Uses `toMaybe` to implement `toJSON` and `toEncoding`, and `aeson`'s `omitField` to specify when the field should be left out. Note that unless the `Possible` value is encoded as an object field it will be `null` even when you have a `Missing` value. _e.g._ `[Missing, HaveNull, HaveData 42]` will be encoded as `[null,null,42]`
Instance details Defined in Data.Aeson.Possible Methods toJSON :: Possible a -> Value # toEncoding :: Possible a -> Encoding # toJSONList :: [Possible a] -> Value # toEncodingList :: [Possible a] -> Encoding # omitField :: Possible a -> Bool #
type Rep (Possible a) Source #
Instance details Defined in Data.Aeson.Possible type Rep (Possible a) = D1 ('MetaData "Possible" "Data.Aeson.Possible" "aeson-possible-0.1.0.0-inplace" 'False) (C1 ('MetaCons "Missing" 'PrefixI 'False) (U1 :: Type -> Type) :+: (C1 ('MetaCons "HaveNull" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "HaveData" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a))))

toMaybe :: Possible a -> Maybe a Source #

fromMaybeMaybe :: Maybe (Maybe a) -> Possible a Source #