Data.Aeson.Possible

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

Constructors

Missing

HaveNull

HaveData a

Instances

Alternative Possible

Similar to the Alternative Maybe instance, picks the leftmost HaveData value.

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

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

Defined in Data.Aeson.Possible

Methods

fmap :: (a -> b) -> Possible a -> Possible b

(<$) :: a -> Possible b -> Possible a

Generic (Possible a)

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)

Defined in Data.Aeson.Possible

Methods

showsPrec :: Int -> Possible a -> ShowS

show :: Possible a -> String

showList :: [Possible a] -> ShowS

Eq a => Eq (Possible a)

Defined in Data.Aeson.Possible

Methods

(==) :: Possible a -> Possible a -> Bool

(/=) :: Possible a -> Possible a -> Bool

FromJSON a => FromJSON (Possible a)

Uses omittedField to default to Missing

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)

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]`

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)

Defined in Data.Aeson.Possible

type Rep (Possible a) = D1 ('MetaData "Possible" "Data.Aeson.Possible" "aeson-possible-0.1.0.1-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

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