Copyright	(C) 2015-2016 Oleg Grenrus
License	BSD3
Maintainer	Oleg Grenrus <oleg.grenrus@iki.fi>
Safe Haskell	None
Language	Haskell2010

Data.Aeson.Extra.CollapsedList

Description

Synopsis

Documentation

newtype CollapsedList f a Source

Collapsed list, singleton is represented as the value itself in JSON encoding.

λ > decode "null" :: Maybe (CollapsedList [Int] Int)
Just (CollapsedList [])
λ > decode "42" :: Maybe (CollapsedList [Int] Int)
Just (CollapsedList [42])
λ > decode "[1, 2, 3]" :: Maybe (CollapsedList [Int] Int)
Just (CollapsedList [1,2,3])

λ > encode (CollapsedList ([] :: [Int]))
"null"
λ > encode (CollapsedList ([42] :: [Int]))
"42"
λ > encode (CollapsedList ([1, 2, 3] :: [Int]))
"[1,2,3]"

Documentation rely on f Alternative instance behaving like lists'.

Constructors

CollapsedList (f a)

Instances

Functor f => Functor (CollapsedList f) Source
Foldable f => Foldable (CollapsedList f) Source
Traversable f => Traversable (CollapsedList f) Source
Eq (f a) => Eq (CollapsedList f a) Source
Ord (f a) => Ord (CollapsedList f a) Source
Read (f a) => Read (CollapsedList f a) Source
Show (f a) => Show (CollapsedList f a) Source
(ToJSON a, ToJSON (f a), Foldable f) => ToJSON (CollapsedList f a) Source
(FromJSON a, FromJSON (f a), Alternative f) => FromJSON (CollapsedList f a) Source

getCollapsedList :: CollapsedList f a -> f a Source

parseCollapsedList :: (FromJSON a, FromJSON (f a), Alternative f) => Object -> Text -> Parser (f a) Source

Parses possibly collapsed array value from the object's field.

λ > newtype V = V [Int] deriving (Show)
λ > instance FromJSON V where parseJSON = withObject "V" $ \obj -> V <$> parseCollapsedList obj "value"
λ > decode "{}" :: Maybe V
Just (V [])
λ > decode "{\"value\": null}" :: Maybe V
Just (V [])
λ > decode "{\"value\": 42}" :: Maybe V
Just (V [42])
λ > decode "{\"value\": [1, 2, 3, 4]}" :: Maybe V
Just (V [1,2,3,4])